The verb rendered I gave solemn warning means much more than merely “testify” (so King James Version), as can be seen by its use in such passages as Luke 16.28; 2 Timothy 2.14; 4.1. It appears in other translations as “urging” (Jerusalem Bible), “most emphatically urged” (Phillips) and “insisted on” (New English Bible). I gave solemn warning may be rendered as “I warned them strongly,” “I said to them with strong words,” or “I spoke to them harshly.” The verb warning may introduce direct discourse—for example, “warned them, You must turn from your sins to God….”

That they should turn from their sins to God, and believe in our Lord Jesus is a summary of Paul’s message. The first part, turn from their sins to God, is literally “repentance with respect to God.” But in biblical thought “repentance” always means “to turn from one’s sins,” and it always presupposes that in so doing one would turn to God. Therefore, within the phrase “repentance with respect to God” there are two clearly implied elements: (1) to turn from one’s sins, and (2) to turn to God. In the Christian sense one “turns from his sins to God” by believing in the Lord Jesus, though the Greek here has these two elements connected as though they were separate and distinct. Believe in our Lord Jesus is literally “belief with respect to our Lord Jesus,” but “belief” is one of those nouns which is basically verbal, that is, “to believe.”

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 .