why is operative sentence, "God bless you! " correct and "God blesses you" incorrect while 'God ' is singular number so we should use here V5. plz explain it.

If you say “God blesses you”, you are saying as a fact that God has delivered such a blessing. Which implies that you can read God’s mind, or God blesses people at your orders. But if you say “God bless you”, you are expressing a wish to that God may deliver a blessing. God, in his wisdom, will decide whether to do as you wish. God bless you” is the lazy version of “May God bless you”, which is a lovely thing to say and you are essentially asking God to bless someone. “God blesses you” means that you think that God blesses (present tense) the person you are speaking directly to … you believe that the person is currently blessed by God.