The Greek phrase “to/in the Lord” makes possible two different interpretations of this verse: (1) it may mean “believers in the Lord joined their group” (so Good News Translation, Moffatt, An American Translation*, New English Bible) or else (2) it may mean “believers were added to the Lord” (so Revised Standard Version, Jerusalem Bible).

The use of a dash in verse 14 makes the second part a kind of parenthetical explanation of the term group. This is, however, very difficult to render literally in some languages. The closest equivalent is often “there were so many men and women….” Though the Greek expression rendered as were added is passive, thus suggesting that the agent may be God himself, most translations omit the specific addition of the agent and therefore employ a phrase such as “joined themselves to” or “became a part of.” This latter expression has the advantage of not indicating specifically whose initiative was involved.

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 .