A.T. Robertson Commentary Acts 21:23

"Do therefore this that we say to thee: We have four men that have a vow on them;" — Acts 21:23 (ASV)

Do therefore this (τουτο ουν ποιησον). The elders had thought out a plan of procedure by which Paul could set the whole matter straight.

We have (εισιν ημιν). "There are to us" (dative of possession as in 18:10). Apparently members of the Jerusalem church.

Which have a vow on them (ευχην εχοντες αφ'-- or εφ' εαυτων). Apparently a temporary Nazarite vow like that in Nu 6:1-21 and its completion was marked by several offerings in the temple, the shaving of the head (Numbers 6:13–15). Either Paul or Aquila had such a vow on leaving Cenchreae (Acts 18:18). "It was considered a work of piety to relieve needy Jews from the expenses connected with this vow, as Paul does here" (Page). The reading αφ' εαυτων would mean that they had taken the vow voluntarily or of themselves (Luke 12:57; 2 Corinthians 3:5), while εφ' εαυτων means that the vow lies on them still.