"I want my lawyer, my tailor, my servants, even my wife to believe in God, because it means that I shall be cheated and robbed and cuckolded less often. ... If God did not exist, it would be necessary to invent him." [Voltaire]
First record of Godawful "terrible" is from 1878; God speed as a parting is from c.1470. God-fearing is attested from 1835. God bless you after someone sneezes is credited to St. Gregory the Great, but the pagan Romans (Absit omen) and Greeks had similar customs.