'O God' in the Bible

Then shalt thou go on forward from thence, and thou shalt come to the plain of Tabor, and there shall meet thee three men going up to God to Bethel, one carrying three kids, and another carrying three loaves of bread, and another carrying a bottle of wine:

And Saul said, Let us go down after the Philistines by night, and spoil them until the morning light, and let us not leave a man of them. And they said, Do whatsoever seemeth good unto thee. Then said the priest, Let us draw near hither unto God.

So and more also do God unto the enemies of David, if I leave of all that pertain to him by the morning light any that pisseth against the wall.