Let us hold fast (katechōmen). Present (keep on holding fast) active volitive subjunctive of katechō as in Heb 3:6, Heb 3:14.
That it waver not (aklinē). Common compound adjective (alpha privative and klinō, unwavering, not leaning, here only in N.T. It is a confession of hope, not of despair.
That promised (ho epaggeilamenos). First aorist middle articular participle of epaggellō. This is the argument remaining to be discussed (10:26-12:3) and already alluded to (Heb 6:13.; Heb 8:6). The ministry of Jesus rests upon “better promises.” How better? God is “faithful,” but he made the other promises also. We shall see.