'O God' in the Bible

Do not rejoice, O Israel, with exultation as do the [pagan] peoples,For you have played the prostitute, turning away from your God.You have loved prostitutes’ earnings on every threshing floor [attributing the harvest to the Baals instead of to God].

Yet I have been the Lord your GodSince [the time you became a nation in] the land of Egypt;And you were not to know any god except Me,For there is no savior besides Me.