How should one approach a Christian Father to help him revert to Islam? What should be the points that would convince a Christian to shun Christianity?
Before answering your questions, I think it would be important to suggest the proper mentality for a matter such as this. When approaching any person of another faith, the most important guidelines to follow are encompassed within the values of sincerity, humility and respect. I believe when engaging with individuals interested to learn more about Islam one should approach the engagement as an opportunity for dialogue, not simply an avenue for conversion. There is unfortunately such a great deal of misinformation and misunderstanding about our religion that even simply correcting these matters through dialogue is an important part of da‘wah. If conversion results from arguments you present, then that is wonderful. However, the other party in the dialogue should not doubt the sincerity of your engagement by suspecting you have other motives. An easy way to judge your approach is to ask yourself how you would feel if a Christian were aggressively trying to convert you to Christianity as compared to simply helping you learn more about it.
With regard to the ‘points’ that should be used to convince a Christian to shun Christianity, a few things should be understood. First, you should not aim to have them shun their faith, but rather find greater truth in yours. After all, the message to those who later became Christians was originally the eternal message of Islam. Only later, were parts of it corrupted. Hence, your general approach should recognize that although there is great value in the teachings of Christianity, Islam is the final revelation that helps correct and complete what came before it. Second, it must be kept in mind that there is no set formula or list of points to be used for all Christians, no matter who they are. That is to assume that all Christians are the same and not give proper weight to the respective backgrounds and contexts that they come from. It is always important to develop a sincere relationship with whoever you are speaking to about Islam, if for no other reason than discovering what parts of Islam they would find most valuable. You are most likely to win someone over by highlighting the strengths of Islam, as opposed to the deficiencies of the Bible.