The Ministry of Apollos in Achaia (18:27-28).
‘And when he was minded to pass over into Achaia, the brethren encouraged him, and wrote to the disciples to receive him, and when he was come, he helped them much who had believed through grace, for he powerfully confuted the Jews, and that publicly, showing by the scriptures that Jesus was the Christ.'
Moving on to Achaia Apollos continued his ministry, but now with the full facts burning in his heart. Now he was indeed fervent in the Spirit. The ‘brethren' in Ephesus, (‘the brethren' suggests that there was already a small church there, possibly founded by Priscilla and Aquila during there stay there), encouraged him in his endeavour, and sent letters with him recommending him to the churches of Achaia. Such letters of commendation were to be a regular feature of the early church in order to identify true men of God, and avoid the danger of false and lying prophets. On arrival there he was a great help to the believers, ‘those who had believed through grace', for he powerfully and publicly demonstrated to the Jews from the Scriptures, that the Messiah was Jesus.
‘Those who had believed through grace.' Compare especially Acts 15:11. See also Acts 4:33; Acts 11:23; Acts 13:43; Acts 14:3; Acts 14:26; Acts 15:40; Acts 20:32. This refers to those who were trusting in the ‘unmerited love and compassion' (grace) of God for salvation through the cross and resurrection of Christ (Acts 15:11), as contained in the word of His ‘grace' (Acts 14:3). ‘Grace' is the unmerited love and compassion of God which was revealed clearly in the lives of the converts at Pentecost and after (Acts 4:33) and in Syrian Antioch when Barnabas visited them (Acts 11:23). Thus the disciples in Pisidian Antioch were ‘encouraged to continue in the grace of God', that is, in trusting in God's unmerited love and favour for their salvation. In Acts 14:26 and Acts 15:40 it refers to God's gracious and effective assistance in the ministry.
Up to this point we are only told that he preached in Achaia, but eventually, as we would expect, Apollo ministered in Corinth (Acts 19:1). How soon it was after his arrival in Achaia we are not told. Possibly almost immediately. He would later return to Ephesus (1 Corinthians 16:12).