hi ,Niallandthepotatoes3....its out of respect. God is important and so is Jesus...and deserves the respect for uppercase letters to address them...and for the word you unless its at the begining of a story,or a letter to someone we use a uppercase letter. or a name, or a place....if you write God's name with a lowercase letter...its referring to a little god...which is also referring to a devil.
The same reason we capitalize certain words--because of their importance. Capitalizing the names of God and Jesus reflect the honor and prestige we attribute to their names. The bible also capitalizes the word God and Jesus and the pronouns that refer to them (He said), so it's possible too that the whole idea of capitalizing God and Jesus may have started here.