The story of Apollos illustrates the fluid situation that could exist in synagogues in different locations at that time. Although John the Baptist had been dead for a couple of decades, there were still groups that held to his message that the coming of the Messiah was near. There was such a group in Ephesus and maybe Apollos was aware of them.
Apollos is a reminder that a person may know a lot and yet not know enough. He seems to have been aware that John had identified Jesus as the Messiah, so perhaps he had heard John in person and then returned to Alexandria with knowing what Jesus did subsequently. In God's providence, there was a couple, Priscilla and Aquila, in Ephesus who told him about what had happened to Jesus after John had baptised him. No doubt Apollos listened gladly to what they said about Jesus.
Apollos, along with Priscilla and Aquila, must have had an effective witness in Ephesus because by the time Apollos left there a number of people had become Christians (the brothers in Ephesus provided him with a letter of commendation). We might have imagined that the Lord would have wanted Paul to plant the church in Ephesus, but he worked otherwise.
Luke, under the guidance of the Spirit, chose not to tell us the areas of misunderstanding that Apollos had, which is a reminder to us that when a person becomes more accurate in the faith there is no reason to keep on referring to his previous inaccuracies in a personal way. Also the fact that Apollos received private instruction from Priscilla and Aquila rather than a public correction indicates that it is better to correct a willing learner in a hidden manner and then not reveal in what ways he had to be helped.
Apollos obviously was able to absorb quickly the additional teaching he required. Three features, however, stand out in his character. First, although highly intelligent and naturally gifted as a speaker, he was marked by humility and was willing to be corrected, even by a woman (which would have been very unusual at that period).
Second, when Apollos spoke about Jesus, he was marked with passion. It is possible to be an eloquent speaker without passion, and merely entertain an audience. Love for the Saviour made Apollos' sermons more than merely pleasant to the ear; in addition, he spoke to the heart with spiritual power.
Third, Apollos was willing to move on to other places and spread the message of Jesus in difficult places. Presumably, Priscilla and Aquila would have told Apollos about the difficulties Paul had experienced from the Jews in Corinth, but that did not deter Apollos from going there to encounter the same opponents with the same message that Paul had declared there.
It is also notable that the brothers in Ephesus, once they had discovered that God was calling their dedicated teacher elsewhere, encouraged Apollos with his plans and helped facilitate them. No doubt, there is a lesson here to a congregation when its effective minister is called to go somewhere else by God.