A question was posed to me, whether or not a Muslim after converted to Christianity should leave Islam. I guess there is something going on called the Insider Movement where this is a big debate. While the answer doesn't seem so complicated, doing it might be. After I got to thinking about, I believe the answer applies to not only former Islam converts but any convert. Coming to Christ, means a new life in Christ. Period. No matter how hard or easy it is. The Bible is pretty plain, "if anyone is in Christ, he is a new creation. The old has passed away; behold, the new has come." (2 Corinthians 5:17) And this doesn't just mean 'new', as in you feel better now, you feel rejuvenated now, you feel alive now, but also 'new', as in different, you are not the same anymore.
Therefore, anyone and everyone who comes to Christ must be different, must leave their former lives behind. When we have a new relationship with Christ, we also by default have a new relationship with everyone else in the world. Especially those once strong unions with people whose ways and beliefs are at odds with what it means to follow Jesus. Fellowship of equal standing with those who are not in Christ when we come to Christ must be severed. The Bible tells us this “do not be unequally yoked with unbelievers… be separate” (2 Cor. 6:14, 17) 1 Cor. 10:21-22 says, “You cannot drink the cup of the Lord and the cup of demons…. Shall we provoke the Lord to jealousy?” Contemplating things of such magnitude should cause one to count the cost of following Jesus.
Do we choose Christ? If we do, we must not look back. Jesus said the one who looks back is not worthy to be his disciple (Luke 9:59-62). We must see all other relationships, all other strong ties as worth giving up compared to gaining Christ (Luke 14:25-33). I do not refer to these scriptures lightly. It is no easy thing to deny yourself, pick up your cross, and follow Jesus. Everything you have ever known will be turned upside down. People may try to shame you; there may be persecution, there may be shunning. And yet Jesus knew all these things would happen. He said in Luke 12:51-52, “Do you think I came to bring peace on earth? No, I tell you, but division. From now on there will be five in one family divided against each other, three against two and two against three.” Which side of the dividing line will we be found? Will we, with trembling knees stand with Jesus, or will we be ashamed of him? Do we count all things as loss in order to gain Christ, or is Jesus only another accessory in our life? Take heart the words of Jesus “If anyone is ashamed of me and my words in this adulterous and sinful generation, the Son of Man will be ashamed of them when he comes in his Father’s glory” (Mark 8:38)
This might lead one to despair. Thinking I can't do this, this sounds too difficult. And you're right, it is. In fact, it is impossible, in and of yourself. But it is not impossible with God (Luke 18:27).
Friends, if you have been saved, you will not only want to leave your former life behind, but the Holy Spirit will guide you the whole way in accomplishing this. Don't get me wrong, this life-changing, old life leaving behind, will take effort, but not effort you work up in your own strength, rather effort that God will empower in you by His Spirit.
God has indwelt you with his Holy Spirit for a reason, not only to change who you are fundamentally at the core of your being but also so you can walk out your newness of who you are. (Ephesians 1:13)
So friends, do not despair, unlesss you have never truly trusted Christ, then indeed you must despair, you must fall on your face and beg God to save you in Christ Jesus. And if you are in Christ, come out from among them, leave your old life behind and follow Jesus. "Examine yourselves, to see whether you are in the faith. Test yourselves. Or do you not realize this about yourselves, that Jesus Christ is in you?—unless indeed you fail to meet the test! I hope you will find out that we have not failed the test.” (2 Corinthians 13:5-6)