1 Thessalonians 1:2

We give thanks to God always for all of you:
Since all things come from God, they first offer thanks for their progress, because God has been pleased not only to give His gift to people who were still in bondage to sin, but also to adopt them as His children, at the same time helping them to put up with all suffering so that they might become worthier.
Keeping the memory of you:
This is because they have grown in the work of faith more than other churches and by God's grace were perfecting the work which they had eagerly begun.

"Grace be unto you, and peace." Do you perceive that the very commencement of his Epistle is with encomiums? "We give thanks to God always for you all, making mention of you in our prayers." For to give thanks to God for them is the act of one testifying to their great advancement, when they are not only praised themselves, but God also is thanked for them, as Himself having done it all. He teaches them also to be moderate, all but saying, that it is all of the power of God. That he gives thanks for them, therefore, is on account of their good conduct, but that he remembers them in his prayers, proceeds from his love towards them.

Immediately after the praise follows glory to God. For by thanking God for them, he shows that they have fulfilled everything by which God is glorified. But at the same time he also teaches humility, since everything is accomplished by God.

That he thanks God is a consequence of their virtues; and that he remembers them in his prayers is due to his love for them.

Rightly he says grace first, then naming peace, because without grace there is no peace nor is reconciliation possible.

Then when Paul says, "we give thanks," he begins the letter's message: first, he commends them for their past perseverance; secondly, he urges them to act well even in the future (4:1). In addition, Paul first gives thanks in general for their blessings; secondly, he remarks upon their blessings in particular matters (1:4). In treating the first point he does two things. First, he offers thanksgiving; secondly, he indicates the reason for the thanksgiving (1:3). Again, Paul first gives thanks for them; secondly, Paul prays for them (1:26).

In treating the first point, Paul mentions three things that ought to be present in thanksgiving. First, thanksgiving should be directed to God: "we give thanks to God." "He bestows favor and honor" (Ps. 84:11). "Every good endowment and every perfect gift is from above, coming down from the Father of lights" (Jas. 1:17). Thanksgiving should be unceasing; so Paul says, "always." It should also be universal, so Paul says, "for you all"; and later Paul adds, "give thanks in all circumstances" (5:18).

Then he prays for them saying: "constantly mentioning you in our prayers"; as if saying: Whenever I pray I am mindful of you: "Without ceasing I mention you always in my prayers" (Rom. 1:9).

This he says twice, just as he says later on in this same letter (5:17).