Neither let us commit fornication (μηδε πορνευωμεν). More exactly, And let us cease practicing fornication as some were already doing (1. Corinthians 6:11; 1. Corinthians 7:2). The connection between idolatry and fornication was very close (see Jowett, Epistles of Paul, II, p. 70) and see about Baal-Peor (Numbers 25:1-9). It was terribly true of Corinth where prostitution was part of the worship of Aphrodite.

In one day (μια ημερα). An item that adds to horror of the plague in Numbers 25:9 where the total number is 24,000 instead Rev 23 as here for one day.