Bound in the spirit. τῷ πνεύματι, may either mean "in my spirit" or "by the Spirit," i.e. the Holy Ghost. If the former, which is the most probable sense (as τὸ πνεῦμα τὸ ἅγιον follows in the next verse), is taken, the sense will be that St.
Paul felt himself constrained to go to Jerusalem. A sense of absolute necessity was upon him, and he did not feel himself a free agent to go anywhere else. If the latter sense be taken, the meaning will be that the Holy Ghost was constraining him to go to Jerusalem.