Jamieson, Fausset and Brown on Revelation 3:9

9. I will make--Greek present, "I make," literally, "I give" (see on Re 3:8). The promise to Philadelphia is larger than that to Smyrna. To Smyrna the promise was that "the synagogue of Satan" should not prevail against the faithful in her: to Philadelphia, that she should even win over some of "the synagogue of Satan" to fall on their faces and confess God is in her of a truth. Translate, "(some) of the synagogue." For until Christ shall come, and all Israel then be saved, there is but "a remnant" being gathered out of the Jews "according to the election of grace." This is an instance of how Christ set before her an "open door," some of her greatest adversaries, the Jews, being brought to the obedience of the faith. Their worshipping before her feet expresses the convert's willingness to take the very lowest place in the Church, doing servile honor to those whom once they persecuted, rather than dwell with the ungodly. So the Philippian jailer before Paul.