Seeing it is a righteous thing with God to recompense tribulation to them that trouble you;
All Commentaries on 2 Thessalonians 1:6 Go To 2 Thessalonians 1
Haimo of Auxerre
AD 865
If indeed,
a conjunction of cause, is used in this case not for the purpose of doubting but for affirmation, as if he were saying, "Since it is just for God to do this."