A.T. Robertson Commentary 1 Corinthians 1:4

"I thank my God always concerning you, for the grace of God which was given you in Christ Jesus;" — 1 Corinthians 1:4 (ASV)

I thank my God (ευχαριστω τω θεω). Singular as in Ro 1:8; Php 1:3; Phm 1:4, but plural in 1 Thessalonians 1:2; Colossians 1:3. The grounds of Paul's thanksgivings in his Epistles are worthy of study. Even in the church in Corinth he finds something to thank God for, though in II Cor. there is no expression of thanksgiving because of the acute crisis in Corinth nor is there any in Galatians. But Paul is gracious here and allows his general attitude (always, παντοτε) concerning (περ, around) the Corinthians to override the specific causes of irritation.

For the grace of God which was given to you in Christ Jesus (επ τη χαριτ του θεου τη δοθειση υμιν εν Χριστω Ιησου). Upon the basis of (επ) God's grace, not in general, but specifically given (δοθειση, first aorist passive participle of διδωμ), in the sphere of (εν as in verse 2) Christ Jesus.