Juristic Reasoning

Scholars of Islam, As-Salamu `alaykum. My question is regarding the perfection of Islam. Can we still claim that Islam is a perfect religion given the fact that, unlike the Qur’an, the Hadiths were not recorded at the time of the Prophet (peace and blessings be upon him) and have been subject to corruption and some of them contradict each other?Can Islam still be free of corruption given that we have ended up with so many different schools of thought (that validate and dismiss various Hadiths depending on their opinions of authenticity)? We believe, for example, that Christianity became corrupted as the Bible was never recorded at the time and was subject to many alterations from priests who were “inspired” by God to change their books. Are we no different by believing that our imams who investigated the authenticity of Hadiths were similarly allowed to find the “truth” by Allah? Jazakum Allah khayran.

Why did the four Imams differ on the same issue? What is the reason behind this difference? Is such difference good for other Muslims? Please enlighten me on this issue.

A week ago, I sent my friend an e-mail asking him if I could educate him about Islam via exchanging e-mails, and he educate me about Christianity. He agreed and since then, I have been sending him information about Prophet Muhammad (peace and blessings be upon him) as well as other Prophets such as Jesus (peace be upon him). N ot only that, but I sent him e-mails about the teachings of Islam as well as information on many other topics. I constantly tell him that I am not trying to criticize or contradict his religion or his beliefs. We don’t get in any arguments or anything of the sort but the most disputed topic is that of Jesus being the Son of God "in human form". I asked him how can Jesus die if he is the Son of God. He says that Jesus was God's Son in "human form". He says that Jesus’ human form died, not his divine form. Well, my question is how can I convince him logically that Jesus (peace be upon him) is not the Son of God but instead only a Messenger of God? I really want you to help me convince him, through some type of reasoning, that Jesus is not the Son of God. I am extremely keen on slowly bringing him toward the light of Islam and my intentions are to slowly change his thinking about Islam and eventually make him convert. Please help me in any way you can.

Dear scholars, As-Salamu `alaykum. Kindly furnish me with details about the concept of Ijtihad, with evidence, please. Jazakum Allah khayran!