…Sanctification must also be understood as an exclusive act of God. Just as forgiveness is exclusively God’s work and every cooperation or conditioning activity on man’s part is completely excluded, so regeneration is an energy that comes simply out of Christ’s victory and does not require our supplementary efforts. It is not fitting to teach justification evangelically and then in the doctrine of sanctification to turn synergistic. Nowhere can we see the gruesome power of “devout” sin as active in theology as at this point. If the “flesh” had to surrender all credit for the origin of faith it again asserts itself all the more emphatically in the continuation of the Christian estate. Man is unwilling to give his honor and gratitude to God alone. From the fact that he is and may continue to be a tool of God he would like to take some credit to himself or even aspires to assist the gratia operans [gracious work] by his own works of penitence and love. The statements in the New Testament, however, make the gift of sanctification dependent, in the same measure as the forgiveness of sins, on faith in Christ, and commands that the message of deliverance be hard and accepted just as gladly and assuredly as the promise of pardon.
– Adolph Koeberle, Quest for Holiness, “Sanctification as the Work of God”, p.95