'O God' in the Bible

We ought always and indeed are morally obligated [as those in debt] to give thanks to God for you, brothers and sisters, as is fitting, because your faith is growing ever greater, and the [unselfish] love of each one of you toward one another is continually increasing.

But we should and are [morally] obligated [as debtors] always to give thanks to God for you, believers beloved by the Lord, because God has chosen you from the beginning for salvation through the sanctifying work of the Spirit [that sets you apart for God’s purpose] and by your faith in the truth [of God’s word that leads you to spiritual maturity].