7. καὶ ἡ ἐλπὶς ἡμῶν βεβαία ὑπὲρ ὑμῶν. The ὑπὲρ ὑμῶν belongs to the whole clause, not to ἐλπίς alone; And our hope is sure concerning you: comp. Php 1:7.
εἰδότες. Because we know. See Ellicott on Eph 6:8. This knowledge gives the sure hope that, when affliction comes, the Corinthians will take it in the right spirit and have their full measure of comfort; ἐστέ is the timeless present, and is not to be understood of the moment of the Apostle’s writing.