What is the meaning of Acts 22:17-21?

17 And it came to pass, that, when I was come again to Jerusalem, even while I prayed in the temple, I was in a trance; 18 And saw him saying unto me, Make haste, and get thee quickly out of Jerusalem: for they will not receive thy testimony concerning me. 19 And I said, Lord, they know that I imprisoned and beat in every synagogue them that believed on thee: 20 And when the blood of thy martyr Stephen was shed, I also was standing by, and consenting unto his death, and kept the raiment of them that slew him. 21 And he said unto me, Depart: for I will send thee far hence unto the Gentiles. (Acts 22:17-21 KJV)

William Burkitt’s Commentary

St. Paul, having thus declared to the Jews his wonderful manner of conversion, proceeds next to acquaint them how desirous he was to have preached to the Jews rather than to the Gentiles, if the will of God had seen fit: but it proved otherwise; for, as he was praying in the temple, he had a vision, in which he was commanded to hasten out of the city, because his former zeal in opposing the gospel would hinder his present preaching of it from being successful. Against this, he humbly argued that his former zeal against Christianity might be an argument to persuade the Jews, his countrymen, to embrace Christianity. But this argument did not prevail for his staying at Jerusalem; but he was commanded to depart from thence, to preach the gospel to the despised Gentiles, who had not such strong expectations against him but would with more readiness embrace his doctrine.

Learn hence, 1. That carnal reasonings are very apt to arise in the hearts of God’s own servants, and cause them to object something against their obedience to the divine commands. Here Apostle Paul objects that according to his reason he saw greater probability of doing good by his ministry among the Jews than he could hope for among the Gentiles, who would be afraid of him, as Ananias was; but Christ repeats his command,  Depart, and get thee hence, for I will send thee to the Gentiles. And now the apostle does no longer dispute but dispatch.

This teaches us, 2. To lay by all our carnal reasonings and vain pretences, when once the call and command of God is clear, and no longer cavil but comply; no longer object but instantly obey. We may safely follow God blindfold when once we have assurance that he goes before us and we should obey his every command without hesitation or limitation.