'O God' in the Bible

We always mention you in our prayers, and give thanks to God for you all:

nor do we fail of giving thanks to God continually, that, when you received the word of God, which we preach, you did not receive it as the doctrine of men, but as a doctrine that appears to be truly divine, by the influences it displays in you, who believe.

how can I be sufficiently thankful to God upon your account, for all the joy, which by your means we have been affected with,

be thankful to God for every thing, for so christians are oblig'd to be.