Albert Barnes Commentary 2 Thessalonians 1:3

"We are bound to give thanks to God always to you, brethren, even as it is meet, for that your faith growth exceedingly, and the love of each one of you all toward one another aboundeth;" — 2 Thessalonians 1:3 (ASV)

We are bound to thank God always for you. (See Barnes' notes on 1 Thessalonians 1:2).

As it is meet. This means it is fit or proper.

Because your faith grows exceedingly. From this, it would seem probable that Paul had heard from them since his first letter was written. He had doubtless received news, at the same time, of the error that prevailed among them regarding his views on the coming of the Lord Jesus, and of the progress the truth was making.

And the charity of every one of you all toward each other. That is, your mutual love.