Note 1 at Acts 23:11: For the Lord to tell Paul to be of good cheer, it can be assumed that Paul needed cheering up. During a previous imprisonment, Paul and Silas cheered up themselves through the power of the Holy Ghost and broke into songs of praise at midnight (Acts 16:25). It can only be speculated what the differences might have been here.

One possible difference might have been Paul's confidence level that he was doing what the Lord wanted him to do. When Paul was thrown in jail in Philippi, he had a vision where he was told to go to that city and preach the gospel (Acts 16:9). Paul was assured that the Lord had sent him to Philippi (Acts 16:10).

In this instance, Paul had received two prophecies warning him against going to Jerusalem (see note 4 at Acts 21:4, p. 700; and note 2 at Acts 21:11, p. ???). It is possible that Paul was contemplating whether or not he had missed God (see note 2 at this verse).

It is true that our ability to rejoice in trying situations is increased when we know that we are in that position at God's leading and not because of our own stubbornness.

Note 2 at Acts 23:11: It cannot be said for sure that Paul was in any disobedience in going to Jerusalem (see note 1 at this verse). However, if there were any questions of whether or not the Lord's blessing was still upon Paul, they were all erased as the Lord Jesus Himself cheered up Paul and reassured him that he would preach the gospel in Rome.

This might lead some to expect that there would be no more problems. The Lord had spoken. However, we find that Paul was left in prison another two years, just to please the Jews (Acts 24:27). At that time, there was another attempt of the Jews to kill Paul (Acts 25:2-3) and Paul finally appealed to the judgment seat of Caesar (Acts 25:10-11). This led to a long and dangerous voyage to Rome where Paul fasted for many days to assure his and those on the ship safety.

Being in the Lord's will does not guarantee us the absence of problems (see note 3 at Acts 16:10, p. 668).