Salam, As mentioned by Nasir in the answer above, the phrase means: "If it weren't for God's mercy, he would have raped her." You can clearly see that it is simply an expression that has a religious connotation rather than a "religious saying". The use of such expressions is not uncommon in Arabic.

if weren't for the "protection" or "caring" of God something bad would've happened to her probably rape but I can't tell for sure until I get an Idea of what the text is about