Note 1 at Acts 18:24: Apollos was a Jew born at Alexandria (see note 4 at Acts 6:9, p. 602) in Egypt. Special mention is made of Apollos' powerful ability to communicate and his knowledge of the scriptures, therefore, they must have been very impressive.

Apollos knew only the baptism of John the Baptist (see note 2 at Acts 19:3, p. ???). This would imply that he received his revelation of the Messiah from John the Baptist but somehow missed the ministry of Jesus Himself, or if exposed to the ministry of Jesus, he left before the establishment of the church on the day of Pentecost. It is possible since Apollos was from Alexandria that Apollos was in Jerusalem for one of the feast when he heard the message and believed, then went back home, thus missing the complete gospel.

Regardless, it is clear that Apollos was preaching that Jesus was the Christ. The thing that was missing was that he was not aware of the ministry of the Holy Spirit. This can be seen by the disciples that Paul encountered on his third missionary journey in Ephesus (Acts 19:1-7). These twelve men were believers in Jesus, but they had never heard of the Holy Ghost. When Paul asked them unto what they were baptized, they answered, "unto John's baptism" (Acts 19:3). This no doubt reflects that they were converts of Apollos during his ministry in Ephesus before Aquilla and Priscilla instructed him.

Therefore, it can be supposed that part of the instruction that Aquilla and Priscilla gave Apollos was about the baptism of the Holy Ghost (see note 6 at Acts 2:4, p. 576). It is also possible that Aquilla and Priscilla shared Paul's revelation of grace with Apollos (v. 27). It is to Apollos' credit that such a powerful man was willing to humble himself and receive instruction (Pro. 9:9).

When Apollos decided to head into Achaia (see note 11 at Acts 18:12, p. ???), the disciples at Ephesus sent a letter to the brethren there exhorting them to receive Apollos and his ministry (v. 27). Apollos was used mightily to preach the gospel (v. 28) insomuch that many of the Corinthians formed a sect around his teachings (1 Cor. 3:4).

Despite the fact that some of the Corinthians used Apollos' teachings to cause a division in the church and discredit Paul, there is no indication that Paul and Apollos ever had a problem with each other or their teachings. To the contrary, Paul greatly urged Apollos to return to Corinth to instruct the brethren (1 Cor. 16:12) and he instructed Titus to help Apollos with anything he needed for his journey (Ti. 3:13).