What does Acts 21:13 mean?

Paul is in Caesarea Maritima on the coast of Judea. He is on his way to Jerusalem. For several months, the Holy Spirit has been warning him and others that when he arrives in Jerusalem he will be imprisoned and afflicted (Act 20:22–23). Fellow Jesus-followers in Tyre and Caesarea have begged him not to go to Jerusalem (21:4, 12). This is his response.

In an earlier letter to the church in Corinth, Paul iterated the hardships he had already endured:

…far greater labors, far more imprisonments, with countless beatings, and often near death. Five times I received at the hands of the Jews the forty lashes less one. Three times I was beaten with rods. Once I was stoned. Three times I was shipwrecked; a night and a day I was adrift at sea; on frequent journeys, in danger from rivers, danger from robbers, danger from my own people, danger from Gentiles, danger in the city, danger in the wilderness, danger at sea, danger from false brothers; in toil and hardship, through many a sleepless night, in hunger and thirst, often without food, in cold and exposure. And, apart from other things, there is the daily pressure on me of my anxiety for all the churches. (2 Corinthians 11:23–28).

Before long, Paul will again be beaten, survive a storm and another shipwreck, and be bitten by a viper (Acts 21:32; 27:13–44; 28:3–5). Eventually, he will be martyred. To the Romans, Paul will write, "For I consider that the sufferings of this present time are not worth comparing with the glory that is to be revealed to us" (Romans 8:18). He will suffer all things for Christ because he knows nothing can separate him from Christ (Romans 8:31–39).