A.T. Robertson Commentary Galatians 2:4

"and that because of the false brethren privily brought in, who came in privily to spy out our liberty which we have in Christ Jesus, that they might bring us into bondage:" — Galatians 2:4 (ASV)

But because of the false brethren privately brought in (δια δε τους παρεισακτους ψευδαδελφους). Late verbal adjective παρεισακτος from the double compound verb παρεισαγω, found in papyri in the sense of brought in by the side or on the sly as here. Evidently some of the Judaizers or sympathizers whom Paul had not invited had come in as often happens. Paul terms them "false brethren" like "the false apostles" in 2 Corinthians 11:13 of the Judaizers in Corinth.

Who came in privily (οιτινες παρεισηλθον). Repetition of the charge of their slipping in unwanted (παρεισερχομα, late double compound, in Plutarch, in N.T. only here and Ro 5:20).

To spy out (κατασκοπησα). First aorist active infinitive of κατασκοπεω, old Greek verb from κατασκοπος, a spy, to reconnoitre, to make a treacherous investigation.

That they might bring us into bondage (ινα ημας καταδουλωσουσιν). Future active indicative of this old compound, to enslave completely (κατα-) as in 2 Corinthians 11:20. Nowhere else in N.T. This was their purpose (ινα and future active indicative of this causative verb). It was as serious a conflict as this. Spiritual liberty or spiritual bondage, which?