1 Corinthians 1:9
God, who has called you into fellowship with His Son Jesus Christ our Lord, is faithful.
What it says
God is faithful, Paul says, and he is the one who called them into fellowship with his Son Jesus Christ.
What it is doing
It grounds the whole thanksgiving in God's faithfulness.
In context
4I always thank my God for you because of the grace He has given you in Christ Jesus. 5For in Him you have been enriched in every way, in all speech and all knowledge, 6because our testimony about Christ was confirmed in you. 7Therefore you do not lack any spiritual gift as you eagerly await the revelation of our Lord Jesus Christ. 8He will sustain you to the end, so that you will be blameless on the day of our Lord Jesus Christ. 9God, who has called you into fellowship with His Son Jesus Christ our Lord, is faithful.