the First Lady Who Became Believer

We are the pioneers and masters of the Arabs, and you have dignity also. My tribe does not deny your virtues, and no one neglects your honor and glory… Our wish was to intermingle with your love and glory. Thus, O Tribe of Quraish! Bear witness that we have married Khadijah (A.S.)to Muhammad (S.A.W.)…"
And it was from there that the union between Muhammad (S.A.W.) – whom no other was like him - and Lady Khadijah (A.S.)– whom carried great honor - was established. It was extremely difficult for the Arabs and the elderly of Makkah to accept this union. They had repeatedly gone to Lady Khadijah's (A.S.)house, yet only returned back with a refusal from Lady Khadijah (A.S.)having ignored their properties, positions and ranks …
This pious woman was more than just a wife in the house of Prophet Muhammad (S.A.W.). She had bid farewell to her comfortable, wealthy, and splendid life. Despite all that, she was happy with her new life. Her previous life was by no means more joyous than her new life, which she spent with her trustworthy husband in love and truthfulness.
And then, Prophet Muhammad's (S.A.W.) mission was commenced Prophet Muhammad (S.A.W.) received the revelation, which obliged him to convey the message to his relatives. (1) Lady Khadijah (A.S.)was the first lady who became believer. The more Prophet Muhammad (S.A.W.) faced rejection from the society; this pious woman would further express her loyalty and sacrifice.
The tribe of Quraish was fed up with Prophet Muhammad's (S.A.W.) invitation, and decided to besiege the Muslims socially and economically. Lady Khadijah (A.S.) had a significant role in regards to this siege. She granted all her wealth to the besieged Muslims. Muslims spent three years in extreme difficulty, and if it were not for the wealth of Lady Khadijah (A.S.), they would have died of hunger.
Lady Khadijah (A.S.)was not just an ordinary wife for Prophet Muhammad (S.A.W.), as she occupied a special place in his heart due to her sacrifices. Thus, whenever appropriate, Prophet Muhammad (S.A.W.) would reiterate her virtues after her demise. 
Once Aisha, daughter of Abubakr, got agitated and said: "Why do you constantly praise her when she was just an old Arab woman, while Allah has granted you (a wife) better than her?"
Prophet Muhammad (S.A.W.), the symbol of patience and tolerance, was deeply hurt and angered by her words. He replied: 
"No! Allah has never granted me (a wife) better than her. When all the people denied my prophetic mission, it was Khadijah who believed me. In the times when the people disbelieved my words, it was Khadijah who called me the truthful. In the times when people besieged me in financial difficulty, it was Khadijah who helped me with her wealth. And it was her who brought a child like Fatimah (A.S.)…" (2)
Three years before Hijrah (migration to Medina), while Prophet Muhammad (S.A.W.) was gravely suffering from Quraish and the others, the light of Lady Khadijah's (A.S.)life went out. At the last moments of her life, Lady Khadijah (PBUH), who had stood as a loyal companion to Prophet Muhammad (S.A.W.) during his mission, was bidding farewell to him. It was extremely difficult for Prophet Muhammad (S.A.W.) to accept this incident, for he was losing a companion who was the best example of loyalty and sacrifice.
The final words of Lady Khadijah (A.S.)before her death were not of less value than all the difficulties she had faced in the way of Prophet Muhammad (S.A.W.). Lady Khadijah (A.S.)told Prophet Muhammad (S.A.W.): 
"O Messenger of Allah! I was negligent of you, and I did not accomplish what you deserved. Forgive me, and if there is something I can wish for now, it is your satisfaction."(3)
Uttering her last words, she took her final breaths full of faith and humble…
(Selection taken from "Woman of the Age of Islam's Appearance", by Muhammad Ali Bahr al-'Uloom, translated to Persian by Muhammad Ali Amini)
Footnotes:
1-"And warn your nearest relations" (The holy Quran, 26: 241)
2- Sunni sources: Mu'jam Kabir al-Tabarni, vol. 23, p. 13- Musnad Ahmad, vol. 6, p. 118- al-Bidayah wa al-Nahayah, vol. 3, p. 158 and …
Shia sources: Bihar al-Anwar, vol. 16, p. 12- Al-Ifsah fil Imamah (by Shaykh Mufid), p. 217 and …