During the first fifteen years of her marriage, Khadija's duties were purely those of a housewife and a mother.
In A.D. 610 Allah Ta'ala chose Muhammed to be His messenger, and since then there was an accession of new duties for Khadija. Now besides being her husband, Muhammed had also become her guide and leader in the two worlds - this one and the Hereafter. She was highly conscientious in her duties as a wife and a mother; now she also became conscientious in her duties as a Muslima and a Momina (=True Believer). She was happy that Allah had picked her husband out of all creation to carry the message of Islam to the world, and she threw herself heart, mind, and soul into his work to make it successful.

Khadija's parents, like the parents of Muhammed Mustafa, had died when she was quite young. She was thus deprived, as Muhammed was, of the parental love and tenderness. She and her husband were both orphaned early in life but both were destined to give their love and tenderness to the orphans of the world. What they lost in the love and tenderness of their parents, they gained in the infinite love and mercy of Allah Ta'ala Himself.
When Khadija entered the house of Muhammed as his wife, she didn't show any interest in finery, in cosmetics, in expensive and exotic gifts etc. After her marriage, she had only one overriding interest, and that was to secure the comfort and happiness of her husband. She secured them by applying all her energy and tenacity. She was comfortable only if he was comfortable, and she was happy only if he was happy. His happiness was her happiness. She was endowed with that rare genius and that deh hand which made the house of her husband a heaven on this earth.

The role that Khadija played after the Proclamation by her husband, of his mission as the messenger of Allah, was vitally important in the history of Islam. As soon as he stepped out of his house, he put himself in the line of fire. The pagans tormented him with their invectives and they hurt him with their hands. Bristling with difficulties as his work was, rowdy and uncouth neighbors made it even more difficult. But as soon as he entered his house, Khadija greeted him with a smile that routed all his sorrows. She spoke words of cheer, hope and comfort and all his anxieties and fears vanished.
Khadija's smiles and her words acted like a balm upon the wounds which the idolaters inflicted upon Muhammed every day. And every day Khadija revived his spirits and restored his morale. Her cheerfulness "cushioned" for him the devastating pressures of external events, and he was able to face his enemies again with new confidence. The only happiness that he ever found in those years of horror and terror, was when he was with Khadija. Sorrows and tribulations came in waves, one after another, threatening to overwhelm him, but she was always there to rebuild his courage and resolution in overcoming them. She was, for him, a psychological "shield" against the trauma of the constantly escalating violence of the Quraysh.

Khadija had the same sense of mission as Muhammed had, and she was just as eager as he was to see Islam triumph over paganism. To her eagerness to see the triumph of Islam, she added commitment and power. This she did by freeing her husband from the necessity of making a living. She thus enabled him to focus all his attention, all his physical energy, and all his time to the advancement of Islam. This is a most significant
contribution she made to the work of her husband as messenger of God. She was the fulcrum that he needed, in the words of A. Yusuf Ali, "all through his vears of preparation." The years before the Proclamation of Islam, were his "years of prepara tion" for the prophethood.

Yusuf Ali

Days and nights he (Muhammed) spent there (in the cave of Hira) with his Lord. Hard were the problems he resolved in his mind, Harder and more cross-grained than the red granite Of the rock around him, - problems not his own, But his people's, yea, and of human destiny, Of the mercy of God, and the age-old conflict Of evil and righteousness, sin and abounding Grace.
(The Holy Quran - Introduction)
It is probable that Muhammed, the Prophet-Designate, systematized and optimized Islam in the cave of Hira. The lineaments of Islam were clearly and unmistakably visible in his personal life long before he formally proclaimed that he was the messenger of God. We do not know exactly how long did the "years of preparation" last for him but by the time he was forty years old, the framework of Islam was ready in his mind.
Time was a basic factor in the systematization of Islam, and Khadija was aware of its importance for her husband in his work. She therefore created an optimal environment in which he could take maximum advantage of time, and make it productive.
Khadija was abundantly gifted with empathy. She anticipated the unspoken wishes of her husband, and went ahead and did what he wished to be done. Twenty-five years of married life had produced exact point-to-point correspondence between her and her husband.
In the year 10 of the Proclamation, Khadija died. The death of a loved one shows the vulnerability of mortal love. But the love of Muhammed and Khadija was not mortal; it was immortal. When Khadija died, Muhammed's love for her did not die. In fact, his love for Khadija not only outlived her but actually went on growing even after her death. Not even the presence, in his house, of nine wives, could inhibit the growth of that love, and his love for her was always struggling to find expression.
If Khadija had shown kindness to someone at any time, and even if she had done it only once, Muhammed Mustafa remembered it, and he made it a point to show the same kindness to that person even after her death, and he did it as often as possible.
In Medina, once an old woman came to see Muhammed Mustafa with some request. He greeted her cordially, showed much solicitude for her welfare, and complied with her request there and then. When she left, Ayesha who was one of his wives, asked him who the old lady was. He said: "When Khadija and I were in Makka, this woman came from time to time to see her."
In her lifetime, Khadija had shown generosity and kindness to countless people. After her death, Muhammed Mustafa did not forget those people. The recipients of the generosity and the kindness of Khadija, became, after her death, the recipients of the generosity and the kindness of her husband. In this connection, Ayesha is reported as saying:
Whenever a goat or a sheep was slaughtered (in the house), the messenger of Allah ordered its meat to be sent to the ladies who at one time had been friends of Khadija. One day I asked him why did he do so, and he said: "I love all those people who loved Khadija."
Allah Ta'ala honored His loving slave, Khadija, and saved her from the anguish of sharing the love of her husband with other women. Throughout the quarter-century of married life, she and she alone was the companion and friend of her husband, Muhammed Mustafa. They lived for each other and they shared the bitters and sweets of life together.

Allah had bestowed many great attributes of character and personality upon His slave, Khadija. As richly blessed as she was with those attributes, she "reinforced" them with good deeds for Islam. She dressed up those attributes through love of Allah, obedience to her husband, and service to Islam. Through love and service, she rose to a position which remained unattainable for any other wife of Muhammed Mustafa.
After the death of Khadija, many other women entered the house of Muhammed Mustafa as his wives. Some of them did little, if anything, to bring cheer, comfort and peace to him. In fact, they did just the opposite. They took cheer, comfort and peace away from him, and brought heart-burning to him.
Khadija alone made, with her chemistry of character, the house of Muhammed Mustafa, the Messenger of Allah, an "island" of peace, contentment and happiness in a sea of conflict and strife.
It was decreed in Heaven that Muhammed Mustafa should marry the most well-born and the most understanding woman in all Arabia. There did not exist such a woman other than Khadija. Allah had a distinct purpose for her to fulfil. Their marriage, thererore, was made in Heaven. Abbas Mahmud al-Akkad of Egypt says in his book, Avesha:
"It was the special decree of Allah that the wife of His messenger should be a woman so sympathetic and pure as Khadija."
Khadija was the embodiment of piety and purity, and she was a guardian of the supreme ideals and the loftiest values in life. It is most probable that if Muhammed Mustafa had not appea~red on the scene, Khadija might have spent her life in the single state. Muhammed Mustafa, the Messenger of Allah, had once said about his daughter, Fatima Zahra, that except Ali ibn Abi Talib, no one was worthy of marrying her. It would be just as true to say that except Muhammed no one else was worthy of marrying Khadija.
In this regard, A. Yusuf Ali, the translator and commentator of Quran Majid, writes as follows:
The only youthful marriage of the holy Prophet was his first marriage - that with Hadhrat Khadija, the best of women and the best of wives. He married her fifteen years before he received his call to Apostleship; their married life lasted for twenty-five years, and their mutual devotion was of the noblest, judged by spiritual as well as social standards. During her life he had no other wife, which was unusual for a man of his standing among his people. When she died, his age was 50, and but for two considerations, he would probably never have married again, as he was most abstemious in his physical life.
The two considerations which governed his later marriages were: (1) compassion and clemency as when he wanted to provide for suffering widows, who could not be provided for in any other way in that state of society; some of them, like Sauda, had issue by their former marriage, requiring protection; (2) help in his duties of leadership, with women, who had to be instructed and kept together in the large Muslim family, where women and men had similar social rights.
Muhammed Mustafa, the Apostle of Allah, welcomed every opportunity to express his admiration, and affection for Khadija, and in acknowledging her great and signal services to Islam. He did so, in the first place, to comply with the commandment of Allah enshrined in the following verses of His Book:

1. AND SOLEMNLY REHEARSE GOD'S FAVORS UPON YOU.
(Chapter 2; verse 231)

2. BUT THE BOUNTY OF THY LORD - REHEARSE AND PROCLAIM
(Chapter 93; verse 11)

Muhammed Mustafa, the slave and messenger of Allah, received many favors and bounties from Him - through Khadija - and he rehearsed and proclaimed them.
In the second place, Muhammed Mustafa liked to restate the great deeds of Khadija in the service of Allah and Islam, out of his love for her. It was one way for him to express love. It was also one way for him to recapture the time he and Khadija had spent together in Makka. One can clearly see that in his reminiscences, he was visiting or rather re-living his past, and one can also discern in them faint traces of nostalgia. There must have been moments in his life, as there are in the life of every individual, when he was overcome by nostalgia.

The authors of two famous books, Isaba and Isti'ab, have quoted Hadhrat Ayesha as saying:
"Whenever the Messenger of Allah left the house to go anywhere, he remembered Khadija; he praised her and he blessed her."

With passing years of married life, the love of Muhammed and Khadija gained in depth and strength. With her love, she banished all his anxieties, fears and sorrows, as noted before. To use an oriental metaphor, Khadija plucked all the thorns out of the life of Muhammed Mustafa, and in their stead, she planted roses of love and tulips of affection. Those flowers never withered; their color, fragrance and freshness were everlasting. If ever there was a marriage that was "evergreen," it was the marriage of Muhammed and Khadija; it was as fresh on the last day as it was on the first. Khadija remained forever alive in his heart. It was her name which was on his lips at all times, and it was her love which filled his heart. Just talking about her and complimenting her made him happy.