All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Undertaking the responsibility of calling non-Muslims to Islam is, indeed, an important and serious issue. The one who decides to do this must know that he needs to exert a lot of effort and have a lot of patience.
First, he must be fully acquainted with his own religion and of the malicious allegations and misconceptions made up by the enemies of Islam and must know how to refute such allegations and misconceptions.
Second, he must learn how to point out the defects and flaws that are found in other religions.
This is essential because the one who ventures into this field without sufficient knowledge and without strong faith would either be subjected to temptation or would at least be defeated. How many a sound and true idea loses its impact because the one who presents it is not qualified to do so and is not fully acquainted with it.
Comparative religion has become an independent science and many books have been written on this subject. We advise the questioner to follow the previously mentioned steps before starting to call non-Muslims to Islam, or else, you may be affected by their malicious allegations and you may fail to adequately refute their false misconceptions.
Moreover, we advise you to listen to the debates of Shaykh Ahmad Deedaat with the Christians.
Allaah Knows best.