The Pulpit Commentary on John 3:24

For John had not yet been cast into the prison. This clause shows that the evangelist was alive to the apparent discrepancy which his account of a Judaean ministry might otherwise have suggested with the synoptic chronological initium of the Galilaean ministry.

The remark shows that all that happened preceded that ministry, and equates the journey through Samaria with that mentioned in Matthew 4:12. Even Hilgenfeld says, "Involuntarily the fourth evangelist here testifies to his acquaintance with the synoptical narrative."

In our opinion it was designed and spontaneous. The first journey to Galilee, mentioned in John 1:43, was not the commencement of a public prophetic ministry, and the synoptists are silent about it. The ἀνεχώρησεν, he "withdrew," shows that there was some reason for his abrupt departure, over and above what was stated.

John gives the reason for the departure by John 4:1, John 4:2, where the conduct of the Pharisees was becoming more watchful and jealous. The authority which John here assumes to correct and enlarge apostolic tradition, reveals the claim of one who professed unique knowledge of inexpugnable facts.