‘Behold, I will make them of the synagogue of Satan, which say they are Jews, and are not, but do lie.’ Were they Jews or not? Yes, they were Jews viewed ethnically, but what Christ means is that they were not Jews in the sense of being of the true Israel, the household of faith.
We do not want people to come and worship at our feet, but it is a strong expression about how the hardest people can be melted down by the Spirit of God and can hear the word and realise it is authentic, be convicted of sin and come to Christ. The promise to Philadelphia is that these wonderful things will happen because they use what strength they had, and God can amplify and magnify it, because they kept his word, and did not make use of worldly methods, and because they did not deny his name.