We were studying Acts 20 last night at church, reading in Acts 20:16 that Paul was heading to Jerusalem, and someone asked, "Why was Paul heading to Jerusalem?"
The answer given in class is that he was going to where he'd find a large gathering of people who might be receptive to the Gospel.
I think this is a true answer, but it must be remembered that this answer is assumed, and is never stated in the text.
A second likely reason is that Jewish men went to Jerusalem to celebrate Passover. Paul was Jewish, and as covered in my last blog entry, he, at least for a time, retained his Jewish habits.
A third reason is specifically stated by Paul in Acts 24:11 -- "to worship". The implication (and that's all it is) is that he was going to Jerusalem to participate in the Jewish Passover worship activities (as opposed to Christian worship activities, which would not have required a trip to Jerusalem).
A fourth reason is also specifically stated by Paul, in Acts 24:17 -- "to deliver alms and offerings to my nation". By "my nation", he might be referring to his Christian brothers and sisters (and we know from other passages that was his task), but the context seems to indicate that he intended his listeners to understand the phrase as referring to the physical Jewish nation, implying that Paul considered the Christians in Jerusalem as part of the physical Jewish nation.
So, Paul was going to Jerusalem:
1. to deliver financial aid to the Jewish church
2. to teach the Gospel (a probable reason)
3. because he was a Jew and that's what Jews did (also a probable reason)
4. to worship.