Writing to the church in Philadelphia, Jesus says,
Behold, I will make those of the synagogue of Satan who say that they are Jews and are not, but lie--behold, I will make them come and bow down before your feet, and they will learn that I have loved you. (Revelation 3:9)
The Christians seem to have been shut out from the synagogue in Philadelphia. Jesus has just assured them that He has the keys of David, and He will let them into the door that really matters, entrance into the kingdom of God. Now, He says that He'll also set straight those who are persecuting them, namely Jews who have rejected Jesus.
Jesus refers to them as "those of the synagogue of Satan" (v. 9). Consider the implications here. Contrary to popular Christian belief, the Jews (who have rejected Jesus) are no longer God's people. They have been broken off (see Romans 11). They belong to the synagogue of Satan. They are actually "not" Jews, "but lie" (v. 9). Romans 2:29 says, "...a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter." Not everyone who was physically a Jew was a true Jew. True Jews, true people of God, are those who have believed in Jesus Christ.
Here is the reversal promised by Jesus: "...behold, I will make them come and bow down before your feet" (v. 9). Whereas now, the Jews were treating the Christians like trash, eventually, they would be at the Christians' feet. When will this happen? When Christ returns to vindicate His people.
Here is the vindication: "...they will learn that I have loved you" (v. 9). The Jews who rejected Jesus and have remained under the illusion that God loves them and rejects Gentiles will one day be shown that His love was actually toward those who trust in Jesus Christ, including the Gentiles who did so. The persecuted will be vindicated when Christ returns.
Jesus provides this as a comfort to these Philadelphian Christians. And we ourselves will experience reversal and vindication also. It's not that we'll be vengeful, arrogant, and sadistic. But we will enjoy the revelation of God's justice and acting on our behalf. Come, Lord Jesus, come.