John Calvin Commentary 1 Thessalonians 5:24

"Faithful is he that calleth you, who will also do it." — 1 Thessalonians 5:24 (ASV)

Faithful is he that hath called you. As he has shown by his prayer what care he exercised regarding the welfare of the Thessalonians, so he now confirms them in an assurance of Divine grace.

Observe, however, by what argument he promises them the never-failing aid of God: because he has called them. By this, he means that when the Lord has once adopted us as his sons, we may expect that his grace will continue to be exercised towards us.

For he does not promise to be a Father to us merely for one day, but adopts us with this understanding: that he is to cherish us always after that. Therefore, our calling should be for us an evidence of everlasting grace, for he will not leave the work of his hands incomplete (Psalms 138:8).

Paul, however, addresses believers who had not been merely called by outward preaching, but had been effectually brought by Christ to the Father, so that they might be among his sons.