Translation:

17. They impress on thee as favor that they have embraced Islam. Say "Count not your Islam as a favor upon me: Nay Allah has conferred a favor upon you that He has guided you to the Faith if ye be true and sincere.

Notes (Tafseer)

4937. Islam in itself is a precious privilege. By accepting it we confer no favour on its preacher or on any community. If the acceptance is from the heart, it is a great favour done to those who accept, that the Light of Allah has entered their hearts and they have received guidance.