2 Corinthians 13:3

ἐπεὶ δοκιμὴν κ. τ. λ.: seeing that ye seek a proof of Christ speaking in me (cf. Matthew 10:20), i.e., a proof that I am really an “Apostle” with a “mission” from Christ to speak in His Name. This last thought leads him into a short digression. “He who has thus commissioned me is not weak, but strong, and this paradoxical strength in weakness is mine also” (2 Corinthians 13:3 b, 2 Corinthians 13:4). ὃς εἰς ἡμᾶς κ. τ. λ.: who is not weak in relation to you, sc., as you think me to be (2 Corinthians 10:10; 2 Corinthians 11:21), but is powerful in your midst. And this is true for two reasons: (a) because of His Resurrection, as the Victor over Death; (b) because of the strength with which He empowers us in the discharge of our duty to you. Each of these reasons is now introduced by καὶ γάρ.