Since it is a righteous thing with God to repay affliction to those who afflict you,
In verse 6 Paul draws a comparison between the law which forbids retaliation to the individual (Romans 12:17), and that which accords it to all government, especially the government of God himself, under whose rule unforgiven iniquity never escapes punishment (Hebrews 2:2; Revelation 20:12). He does this to show that God is under the second and not under the first law. In verse 7 we are reminded that the negative happiness of heaven is rest from all afflictions, sorrows, pains, persecutions, etc. (Hebrews 4:9; Revelation 14:13; Revelation 21:4) (McGarvey and Pendleton 31-32).