I hesitate to ask, but...is Jesus's teaching about the Kingdom of Heaven therefore not relevant, applicable, to everyone, us?
The question is when did "Time Past" end and "But Now" begin?
Verses 13-22 answers that question. When the middle wall of partition between Jews and Gentiles was taken down, and we were made one, is when "but now" began.
That means that while the middle wall of partition was up, it was "time past". Hebrews 9:16,17 tell you that as long as the testator lives, the testament is of no strength. Which means that Christ's earthly ministry was part of "time past". Why do you think He told the disciples to "go NOT unto the way of the Gentiles"? And "I am NOT sent but unto the lost sheep of Israel." ? It was the Kingdom that was being preached, Christ as Messiah, and the setting up of Israel as a nation of priests to the gentile nations. Once she accepted Christ as Messiah. But we know she did not. Only the little flock.
"but now" involves a body of believers, not a kingdom of believers. It began with Paul, and it ends with the rapture of the body of Christ. Then comes the "ages to come", the tribulation, the 2nd coming of Christ, the setting up of the Kingdom, the 1000 year reign, the unloosing of Satan for a season, the final judgement, etc.
Christ's teaching about the Kingdom of Heaven was taught to whom? Israel. Who were commissioned to teach the nations. But we now know the history of that. And WHY Paul was saved and given his commission.