2 Thessalonians 1:3-4 KJV
We are bound to thank God always for you, brethren, as it is meet, because that your faith groweth exceedingly, and the charity of every one of you all toward each other aboundeth;
So that we ourselves glory in you in the churches of God for your patience and faith in all your persecutions and tribulations that ye endure:
Paul gave two reasons to be thankful for these Christians and one reason he boasted about them to others:
Because their faith grew exceedingly
“Their faith was not a faith of miracles, nor a mere historical faith, or a counterfeit and temporary one, but the faith of God's elect; which is the evidence of things not seen, of an unseen Christ, and the glories of another world; that grace by which a man goes out of himself to Christ for righteousness, life, and salvation; by which he is justified, and by which he lives on Christ, and walks on in him as he has received him.”
Because their charity abounded
This charity was “toward each other.” I take the position that charity is a unique sort of love a Christian has for his or her church. These Christians abounded in that charity.
Because of their patience and faith during persecution and tribulation
Paul assured them that their suffering was a token of the judgment of God and that it would be returned upon those who had persecuted them. Suffering is never pleasant. But to patiently endure it for Christ's sake, believing that God will use it for His own glory and to not strike back for our own protection; this is something all heaven takes note of.