Seeing it is a righteous thing with God to recompense tribulation to them that trouble you;
Seeing (that) it is a righteous thing - justifying the assertion that there is a "righteous judgment" (2 Thessalonians 1:5); 'seeing that х eiper (G1512), if, as we all admit: if so be that] it is a righteous thing with х para (G3844), Theoo (G2316): at the tribunal of] God.' Our innate feeling of what is just confirms what is revealed.
Recompense - requite in kind; namely, tribulation to them that trouble you (affliction to those that afflict you); and to you who are troubled, rest from trouble.