William Burkitt on 2 Peter 2:20

By escaping the pollutions of the world, understand their renouncing of them in baptism; their conversion from Heathenism to the profession of Christianity, by the knowledge of the gospel. Now, if afterwards they return to it again, and are intangled in their idolatry, and other gross sins, their latter end is worse than their beginning, their Christian Heathenism worse than their old Heathenism.

Learn hence, That a person may forsake many gross and scandalous sins, and have a visible change and reformation wrought in his life; but, not being a thorough and prevailing change, he is still in an unsafe state; his latter end may be worse than the beginning.