'O God' in the Bible

For from you the word of the Lord was proclaimed not only in Macedonia and Achaia, but your faith with respect to God went into every place, so that we had no need to say any thing;

for they declare of us what introduction we had to you, and how you turned from idols to God, to serve the living and true God,

For what thanksgiving can we render to God for you for all the joy with which we rejoice on your account before our God,