Four Reasons for the Later Marriages

Number one, forging alliances with different tribes. Studying the marriage life of Muhammad (peace be upon him) requires looking at his life comprehensively. The Messenger of Allah, Muhammad (peace be upon him), devoted all of his efforts—every one of them—for the promotion of Islam. Everything that he would do, even his decision in marriage, would be based on the benefit of Islam. Whatever Muhammad (peace be upon him) did in his life, the intention of it was to promote the religion of Allah. He wouldn't do anything purely to satisfy his human desires; he would do it to please Allah (swt). His marriage life is to be read in this light. He married a few of his wives to forge alliances with different tribes, to bring them closer to Islam, like his marriage to Juwayriyyah, which ended up making the whole tribe of Banū al-Muṣṭaliq become Muslim.

Number two, caring for his companions, his followers, like the example of Sawdah (may Allah be pleased with her) given earlier. Number three, Muhammad (peace be upon him) wanted to strengthen his ties with his closest companions. Muhammad (peace be upon him) had a strong brotherly feeling towards his companions, and there was a special group among them whom Muhammad (peace be upon him) wanted to have a stronger relationship with, and that is not only an Islamic brotherhood, but to add to it family ties. And for someone who didn't experience Islamic brotherhood, it's difficult for them to appreciate this. What if you have lived, like Muhammad (peace be upon him), with his companions for twenty-three years? What bond would develop between them? They were, subḥāna Allāh, together in moments of ease and moments of difficulty, on the battlefield and in times of peace. They would eat together, they would travel together. The relationship that Muhammad (peace be upon him) had with the Ṣaḥābah (may Allah be pleased with them) was so strong. In the Madīnah era, when Muhammad (peace be upon him) passed away, the feelings that were in Madīnah, the feelings of loss that the people of Madīnah had, are something that can hardly even be described.

So Muhammad (peace be upon him) wanted to strengthen the relationship between him and his close companions. So Muhammad (peace be upon him) married the daughter of Abū Bakr, and he married the daughter of ʿUmar ibn al-Khaṭṭāb, and he married his daughter to ʿUthmān ibn ʿAffān. And when this daughter of Muhammad (peace be upon him) passed away, he married ʿUthmān another of his daughters, and then she passed away. Muhammad (peace be upon him) said, "If I had ninety-nine daughters, I would marry them to ʿUthmān, one after another." Muhammad (peace be upon him) wanted to have this relationship between him and ʿĀʾishah bint Abī Bakr, and he married his most beloved daughter, Fāṭimah (may Allah be pleased with her), to ʿAlī ibn Abī Ṭālib. So now he had a family relationship between him and the four khalīfahs: Abū Bakr, ʿUmar, ʿUthmān and ʿAlī.