Acts 21:26
Then Paul took the men, and the next day purifying himself with them entered into the temple, to signify the accomplishment of the days of purification, until that an offering should be offered for every one of them. Then Paul took the men, and the next day purifying himself with them entered into the temple, to signify the accomplishment of the days of purification, until that an offering should be offered for every one of them.
Paul took this course in harmony with the counsel given him by the elders. The men he took were four Christian believers at Jerusalem who were under the Nazarite vow. The term of their vow was then nearly expired, almost complete. He entered the temple with them the next day after purifying himself with them, to signify the accomplishment of the days of purification until an offering should be made for every one of them. In doing this he united with them in the ceremonies of the seven days of purification.
The sacrifices required for purification to complete the vow were costly. The expense was beyond what a very poor man could afford, and it was counted a pious act for another to bear the cost for poorer brethren. Those required offerings had not yet been presented. Though Paul himself was poor and labored with his own hands for his daily bread, he willingly paid the whole cost for all four.