And put no difference between us and them, purifying their hearts by faith. Acts 15:9
Faith on the finished work of Christ is the only source to purification. From the light of Acts 15:6-11 this can be done by implanting faith in them, and leading that faith to the blood of Christ, which cleanses from all sin, original and actual, with which men are defiled; for this faith must be connected to Christ redemptive sacrifice on the cross. Good works or doctrines of abstinence does not purify or make any man just before God Colossians 2:20-23, faith that imbibe from grace is the only source of purification.