I.e., participating in their Nazarite vow (see note Acts 21:241a). To do this Paul had to enter into the temple and remain there with the Nazarites until the completion of the seven days of the vow; then the priest would offer the offerings for each one of them, including him. Surely he was clear that such a practice was of the outdated dispensation, which, according to the principle of his teaching in the New Testament ministry, should be repudiated in God's New Testament economy. Yet he went through with it, probably because of his Jewish background, which had also been manifested earlier in his private vow in Acts 18:18, and probably because he was practicing his word in 1 Cor. 9:20. However, his toleration jeopardized God's New Testament economy; this God would not tolerate. At this point he must have felt that he was in a predicament, and he must have been deeply troubled, longing to be delivered from it. Just at the time when their vow was to be concluded, God allowed an uproar to rise up against him, and what they intended to accomplish was blown away (v. 27). Moreover, by God's sovereignty Paul was rescued out of his predicament.
The mixing of Judaic practices with God's New Testament economy was not only erroneous in relation to God's dispensation but also abominable in the eyes of God. This gross mixture was terminated by Him a mere ten years or so later with the destruction of Jerusalem and the temple, the center of Judaism, through Titus and his Roman army. This rescued and absolutely separated the church from the devastation of Judaism.
God might have tolerated Paul's carrying out of a private vow in Acts 18:18, but He would not allow Paul, a vessel chosen by Him not only for the completing of His New Testament revelation (Col. 1:25) but also for the carrying out of His New Testament economy (Eph. 3:2, 7-8), to participate in the Nazarite vow, a strict Judaic practice. In going to Jerusalem, Paul's intention might have been to clear up the Judaic influence on the church there (see note Acts 19:211a, par. 2), but God knew that the church there was incurable. Hence, in His sovereignty God allowed Paul to be arrested by the Jews and imprisoned by the Romans that he might write his last eight Epistles (see note Acts 25:111c), which completed the divine revelation (Col. 1:25) and gave the church a clearer and deeper view concerning God's New Testament economy (Eph. 3:3-4). Thus, God left the Judaism-influenced church in Jerusalem to remain as it was until the devastating mixture was terminated with the destruction of Jerusalem. For Paul to write his last eight Epistles to complete God's New Testament revelation was far more important and necessary than for him to accomplish some outward works for the church.