Brother: as found in brother Apollos, see comments on verse 11. On Apollos himself, see comments on 1.12.

Strongly and “often” are equally possible meanings of the Greek, and the context gives no help in choosing between them.

Brethren as usual means “fellow Christians.”

Most translations agree with Revised Standard Version and Good News Bible in linking to visit you with the other brethren, but the translation “I have more than once encouraged him, together with the other (brothers), to go to you” (Bijbel in Gewone Taal) is also possible, implying that Paul also encouraged others to go. New Revised Standard Version has “the other brethren”; Revised English Bible “the others.”

The following words it was not at all his will do not make it clear in Greek whether Paul means God’s will or Apollos’, as the footnotes in Revised Standard Version and Good News Bible show. Paul’s language may be deliberately indirect in referring to a strong expression of Apollos’ will, with which Paul himself may not have agreed. Revised Standard Version and Good News Bible‘s solution seems best.

When he has opportunity: “when he gets the chance” (Good News Bible) is a common language English rendering of this phrase.

Quoted with permission from Ellingworth, Paul and Hatton, Howard A. A Handbook on Paul’s First Letter to the Corinthians, 2nd edition. (UBS Handbook Series). New York: UBS, 1985/1994. For this and other handbooks for translators see here .