Here is how Wesley himself dealt with the issue of sinfulness remaining in believers: V. 1. The sum of all is this: There are in every person, even after he is justified, two contrary principles, nature and grace, termed by St. Paul the flesh and the Spirit. Hence, although even babes in Christ are sanctified, yet it is only in part. In a degree, according to the measure of their faith, they are spiritual; yet, in a degree they are carnal. Accordingly, believers are continually exhorted to watch against the flesh, as well as the world and the devil. And to this agrees the constant experience of the children of God. While they feel this witness in themselves, they feel a will not wholly resigned to the will of God. They know they are in him; and yet find an heart ready to depart from him, a proneness to evil in many instances, and a backwardness to that which is good. wesley.nnu.edu/john-wesley/the-sermons-of-john-wesley-1872-edition/sermon-13-on-sin-in-believers/