Numbers 6:19
And the priest shall take the sodden shoulder of the ram, and one unleavened cake out of the basket, and one unleavened wafer, and shall put them upon the hands of the Nazarite, after the hair of his separation is shaven: And the priest shall take the sodden shoulder of the ram, and one unleavened cake out of the basket, and one unleavened wafer, and shall put them upon the hands of the Nazarite, after the hair of his separation is shaven:
The verse belongs to the closing ritual of the Nazarite vow, setting forth what was done to complete or end the period of separation. After the hair of separation was shaved, the priest took the boiled or sodden shoulder of the ram together with one unleavened cake and one unleavened wafer out of the basket and placed them upon the hands of the Nazarite. These were offerings connected with the completion of the vow, forming part of the appointed ceremony for finishing it.
That completion required sacrifices for purification, and the prescribed offerings made the ceremony costly. Paul met that expense for four poor Christian Nazarites, joining with them so that they could fulfill and finish their vows.