That phrase indicates (see on Revelation 1:13) that he sets the wick in each church so that each church shines optimally. To set the wick well also implies that Jesus knows the needs of each church. By using this self-description at the beginning of his letter to the church in Ephesus, Christ assures them that they hold no secrets from him. Moreover, by using this self-description in the first of these seven letters (for they all receive a copy of the whole book), he assures all seven churches that he knows precisely what each church needs.
1 “To the angel of the church in Ephesus write: ‘The words of him who holds the seven stars in his right hand, who walks among the seven golden lampstands.