'O God' in the Bible

But [in the meantime] the people were still sacrificing [to God] on the high places (hilltops) [as the pagans did to their idols], for there was no [permanent] house yet built for the Name of the Lord.

So God said to him, “Because you have requested this and did not ask for long life or riches for yourself, or the death of your enemies, but you asked discernment for yourself to understand justice,

And he said, LORD God of Israel, there is no God like thee, in heaven above, or on earth beneath, who keepest covenant and mercy with thy servants that walk before thee with all their heart:

And now, O God of Israel, let thy word, I pray thee, be verified, which thou spakest unto thy servant David my father.

Then Jezebel sent a messenger unto Elijah, saying, "So do God to me, and so thereto, except I make thy soul like one of theirs by tomorrow this time."