wHY dO wE saY "bLEss U"??

I like to choose ‘BLESS’ as a topic for my task two. Three words which i did not understand in this topic are interjection, indulgent, and distinctive. About this topic, Many Americans like to say "God bless you" to the person after he or she sneezes. But not for Muslims, we prefer says "praise to Allah" when someone sneezes. Beside that's we can bless your mother when Mother's day. In "BLESS" topic, I was just asking why people say like that? but know i know that it means for god to protect them from illness. so, that's all 4 task 2. See u later and.... God bless u!!!bye!!