Although it is possible to understand he in the clause he commanded as a reference to God, it is more probable that the reference is to Jesus.
The verb which most translators render “preach” or “proclaim” is expanded by the Good News Translation to preach the gospel, since this is a technical term in the book of Acts for the proclamation of the gospel.
The living and the dead is a comprehensive term for all persons, past and present. It is, of course, part of the teaching of the New Testament that at the end of time some people will still be alive on the earth.
Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on The Acts of the Apostles. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .