Khadijah is known for being Mecca's most powerful women. How did she use her political power and influence to support Muhammad so he could preach?
I would not call it political power as the brother has already rightly pointed out in his comment, but it was not only wealth and noble lineage either. Her whole character supported the Message of Islam. She did not only give her wealth to the Prophet for him to be free from earning a living and to preach the message but she herself took care of the believers by providing them with food, shelter, money and moral support. Giving support to the poor, the widows, the orphans, the sick and the disabled was part of her personality and not influenced by the Prophet, as she did this even before her marriage.
As we know, Khadijah was a very successful business woman and even though the Arab society at that time looked down upon women and treated them more like cattle than human beings, she was highly respected so that the Meccans called her Ameerat-Quraysh ("Princess of Quraysh"), al-Tahira ("The Pure One") and Khadija Al-Kubra (Khadija "the Great"). Why was she called "The Pure One" if not for her impeccable character and flawless behaviour.
Khadija was the image of the perfect soul. Muhammad Mustafa found only four perfect women in the entire human race. Out of these four, the last two belong to the same house; they are Khadija, the mother, and Fatima, her daughter.
She was the first person to testify "La illaha illallah, Muhammadun Rasoolullah" to the truth of the Holy Prophet. And in the years which followed, she was a source of comfort and consolation to the Holy Prophet in his struggle to spread the message and to change the society they were living in completely.
She was, for him, a psychological "shield" against the trauma of the constantly escalating violence of the Quraysh.
For 25 years she was the only wife of the Prophet, which is quite astonishing when we take into account that the Prophet took several wifes after her. This fact shows the deep and loving relationship both found in their marriage. Khadija was the perfect wife always supporting her husband and his mission. She exchanged her life of ease and comfort willingly to a life of austerity, when she suffered the same hardships as the other believers under the economical siege of the Quraish for three years. More than that, she showed her quality as a true "Mother of the believers", when she put their interests over her own by making sure that they had shelter, water and food.
The support that Khadija gave to the Muslim community in Makka, was indispensable for the survival of Islam. Her support to the Muslim community guaranteed its survival when it was in a state of blockade. In this sense, she was a maker of history -the history of Islam.
The Prophet always maintained his special relationship to Khadijah even after she had died.
In al-Bukhari, vol.3 we find the following ahadith :
Ayishah said: "I never envied any woman as much as I envied Khadijah. The Holy Prophet always remembered her. Whenever any sheep or goat was slaughtered, the choicest parts were sent to Khadijah's relatives and friends. I used to say, 'It appears that Khadijah was the only woman in the world.' Hearing this, the Holy Prophet was very much annoyed and said: 'Khadijah had many virtues, which others do not have. "' She also said: "Once the Holy Prophet remembered her and I said, 'How long will you go on remembering a woman so old that she had no teeth in her mouth? Allah has given you a woman better than her (meaning herself).' The Holy Prophet was so angry that the hair of his head was raised. He said: 'By Allah, I do not have better than Khadijah. She believed in me when others were steeped into infidelity. She testified to my truth when others rejected my claim. She helped me with her wealth when others deprived me. And Allah gave me children by her." 'Ayishah says that from then on she decided not to say any unkind word about Khadijah.