Who was Apollos?
(NASB) Acts 18:24-26 “Now a Jew named Apollos, an Alexandrian by birth, an eloquent man, came to Ephesus; and he was mighty in the Scriptures.
25 This man had been instructed in the way of the Lord; and being fervent in spirit, he was speaking and teaching accurately the things concerning Jesus, being acquainted only with the baptism of John;
26 and he began to speak out boldly in the synagogue…”

Apollos was “right on” about the words of Scripture…he had been taught well, and it is implied he studied the Scriptures for himself, he knew them and God’s purposes through them.  However, there was one thing he lacked, and that was the knowledge of the Holy Spirit Who had been sent to believers on the Day of Pentecost in Jerusalem.  (Acts 2:1-13)

Apollos knew of the baptism of John (the Baptist).  It was the baptism of repentance.  John the Baptist had told people they needed to repent for the coming of the Messiah.

What Apollos missed was what else John had said:
(NASB) Matthew 3:11 “As for me, I baptize you with water for  repentance, but He who is coming after me is mightier than I, and I am not fit to remove His sandals; He will baptize you with the Holy Spirit and fire.”

This was fulfilled on the Day of Pentecost when all believers in a room in Jerusalem were baptized with the Holy Spirit.  All believers receive God the Holy Spirit when they acknowledge Jesus Christ as their Lord (Master) and believe that God raised Him from the dead.

Rejoice!  We have a living Savior!  Praise to our God!

As Apollos was speaking in the synagogue, there was a couple there, listening and worshiping God.  Priscilla and Aquila heard him.
Clearly Apollos knew Scripture.  He believed that Jesus was the Messiah Who fulfilled the prophecies.  [Jesus will come a second time, as King, and He will complete the fulfillment of the prophecies in the Old and New Testaments.]
Clearly Apollos did not know about the baptism of the Holy Spirit.  He did know of the baptism of repentance which John the Baptist had given.

Priscilla and Aquila met with Apollos privately.  They explained the baptism of the Holy Spirit, which was given after the ascension of Jesus into heaven.  (Acts 18:26)

Apollos was Scripturally sound.  Are you?
He was teachable.  Are you?