More correctly touching. Comp. Rom 9:27; 2Co 1:8. Ὑπὲρ never in N.T. in a formula of swearing.
Gathering together (ἐπισυναγωγῆς)
Only here and Heb 10:25. The verb ἐπισυνάγειν is used, as the noun here, of the Lord's gathering together his elect at his coming. See Mat 24:31; Mar 13:27; comp. 2 Macc. 2:7.