Though the Samaritans had been baptized in water (v. 12), the gift of the Holy Spirit was delayed until Peter and John came and laid their hands on them. Normally the Spirit is given at the moment of faith (see Acts 10:44; 19:2; Eph. 1:13). In this instance, however, it was imperative that the Samaritans be identified with the apostles and the Jerusalem church so that there would be no rival Samaritan Christian church because of the long-standing rivalry that had existed between the Jews and the Samaritans. Without this delay and the coming of the apostles there would have been an immediate rift or division in the early church. The delay of the baptism of the Spirit (which joins us into union with Christ making us one people [1 Cor. 12:12-13]) until the coming of the apostles, clearly demonstrated their oneness.
The Samaritan believers had been baptized in water as an evidence of their faith and it is this that identified them as Christians. But isn’t a Christian defined as one in whom the Spirit dwells? No, nowhere in Scripture is a believer defined as one in whom the Spirit dwells. One is a believer (a Christian) because of his or her faith in Christ. Indwelling is, of course, just one of the ministries that occurs when one believes, like regeneration and the baptizing work of the Spirit. While it is true that a believer is one in whom the Holy Spirit dwells (Rom. 8:9), withholding the Spirit until the apostles arrived was an exception to the norm, in order to protect the unity of the body of Christ.
Universal indwelling of the Holy Spirit evidently did not exist in the Old Testament because indwelling at that time was both selective and temporary. In the Old Testament the Holy Spirit was with believers in some special way, but not in them as is the case today (see John 14:16-17). But this did not mean they were not believers or saved as was clearly the case even with the disciples themselves. Evidently then, this situation at Samaria was unique and temporarily fell into the category of Old Testament times.
Luke specifically tells us several things which validate, I believe, the above position:
1. They had received the word of God which refers to their faith in the gospel message about Christ and as evidence of this, they had been baptized in water.
2. Then the Jewish apostles (Peter and John), who previously would have had nothing to do with Samaritans, were sent to these Samaritan believers because there was something obviously wrong.
3. The reason given is that, contrary to the norm, they had not received the Holy Spirit. In keeping with what was normal, this was seen as a condition or problem that needed to be rectified, but the reason was undoubtedly the protection of the unity of the Spirit (see Eph. 4:1f).
4. Immediately, as the apostles laid their hands on these new converts (a sign of identification and oneness with these Samaritan believers), the Spirit began indwelling them.