Paul asks his readers to look back honestly at their old life. He does not argue from theory but from their own experience. Barnes says believers have "tasted its bitterness; they have reaped its fruits," so they know firsthand what sin gives. The question presses them to admit that sin left them nothing worth keeping. Gill's answer to the question is direct: "Sin yields no real profit to the servants of it." Their present shame is itself part of the answer.

Paul answers in the same breath: "for the end of those things is death" (Romans 6:21). Then he sets the new life beside the old: "But now being made free from sin, and become servants to God, ye have your fruit unto holiness, and the end everlasting life" (Romans 6:22). He sums it up: "For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord" (Romans 6:23).

"Fruit" is one of Paul's key pictures in this part of Romans. He contrasts fruit "unto holiness" (Romans 6:22) with fruit "unto death" (Romans 7:5), and says believers are joined to Christ "that we should bring forth fruit unto God" (Romans 7:4). The question asks what kind of harvest their old way of life produced.

The ESV makes the time contrast clear: "what fruit were you getting at that time." The "then" of their past stands against the "now" of their shame and their new freedom (Romans 6:21-22).

This question exposes the false promise of sin. Matthew Henry writes that "the present pleasure and profit of sin do not deserve to be called fruit," and that "Shame came into the world with sin, and is still the certain product of it."

But Paul does not leave his readers in shame. The shame belongs to people who are "now" free (Romans 6:22). God replaces the old harvest with a new one, "fruit unto holiness" (Romans 6:22), and gives what no one can earn: "the gift of God is eternal life" (Romans 6:23). The look back is meant to make the gift shine.