Till I make (heōs an thō). Second aorist active subjunctive of tithēmi with an after heōs for the future, a common Greek idiom. This dominion of Christ as Mediator will last till the plan of the kingdom is carried out (1Co 15:23-28). Complete subjugation will come, perhaps referring to the custom of victorious kings placing their feet upon the necks of their enemies (Jos 10:24).
Therefore assuredly (Asphalōs oun). Assuredly therefore, without any slip or trip (asphalēs from a privative and sphallō, to trip, to slip. Peter draws a powerfully pungent conclusion by the use of the adverb asphalōs and the inferential conjunction oun. Peter’s closing sentence drives home the point of his sermon: “This very Jesus whom ye crucified (note humeis, strongly emphatic ye), him God made both Lord and Messiah” (kai kurion kai Christon), as David foretold in Psa 110:1-7 and as the events of this day have confirmed. The critics are disturbed over how Luke could have gotten the substance of this masterful address spoken on the spur of the moment with passion and power. They even say that Luke composed it for Peter and put the words in his mouth. If so, he made a good job of it. But Peter could have written out the notes of the address afterwards. Luke had plenty of chances to get hold of it from Peter or from others.