Calvin on Remaining Sin in the Regenerate

Helpful realism from the reformer--

The children of God are freed through regeneration from bondage to sin. Yet they do not obtain full possession of freedom so as to feel no more annoyance from the their flesh, but there still remains in them a continuing occasion for struggle whereby they may be exercised; and not only be exercised, but also better learn their own weakness. . . . [T]here remains in a regenerate man a smoldering cinder of evil, from which desires continually leap forth to allure and spur him to commit sin.

In regeneration, Calvin goes on to say,

the sway of sin is abolished in them. For the Spirit dispenses a power whereby they may gain the upper hand and become victors in the struggle. But sin ceases only to reign; it does not also cease to dwell in them.

--John Calvin, Institutes, 3.3.10-11

Sin dwells, but no longer reigns, in believers.