I was flipping The Holy Spirit, one of the books by Gordon Clark I haven’t read fully, and came across a section in his chapter on sanctification (pgs. 46-48) which shows he believed sanctification is a synergistic or cooperative process in the same manner as I do (link). Sanctification is a struggle. It requires our "activity" and that we "do" that which God's law commands. In this sense we "cooperate" with God's determinate and efficient grace:
That sanctification is a struggle is plainly stated in Scripture. Romans 7:23 and its context show how Paul struggled. Note that he is here describing his experiences after regeneration. He could not earlier have said, “I delight in the law of God after the inward man.” The phrase in 2 Corinthians 10:3, “For though we walk in the flesh, we do not war after the flesh,” indicates a war. Paul here makes a play of words by using flesh in two different senses First Timothy 1:18 describes Timothy’s sanctification as a good warfare. And in 6:12 Paul urges him to “Fight the good fight of faith.” See also 2 Timothy 2:3.
But the fullest statement that the Christian life is a warfare comes in Ephesians 6:10-17. The whole armor of God is needed to withstand the wiles of the devil; we wrestle against the rulers of darkness; we need a breastplate, a shield, a helmet, and especially a sword. And we need perseverance.
The theologian today and the man in the pews must recognize that this warfare is conducted in the power of the Spirit. Were not the right man on our side, our striving would be losing.
But there is a difference between regeneration and sanctification. As to the former, “we are altogether passive therein.” In the latter we struggle. One must not deny either the Spirit’s power or our activity.
Certain popular Bible teachers have been so impressed by the power of the Spirit that they deny our need to struggle. When I was a boy, my aunt, previously a missionary to the Mormons, gave me Hannah Smith’s The Christian’s Secret of a Happy Life. Fortunately I was too young to understand it. Somewhat hypocritically, as it seems to me now, Mrs. Smith wrote in her Preface, “I do not want to change the theological views of a single individual. The truths I have to tell are not theological, but practical” (p. vi). When she adds, “They will fit in with every creed, she is certainly asserting a falsehood.
The Keswick movement, of which I think Mrs. Smith and her husband were a part, used such phrases as “Let go, and let God”; “We must not try to sin”; “Let him do it all.” For example, Mrs. Smith declares, “Man’s part is to trust, and God’s part is to work…. Either we must do it for ourselves, or someone must do it for us… it is something we are unable to do…. Plainly the believer can do nothing but trust…. Surrender and trust… is positively all the man can do We do not do anything, but He does it” (p. 29-31).
As a dedicated, and many will say extreme, Calvinist, I more than gladly insist on God’s doings. No one understands much of the Bible unless he believes in sovereign predestination. But if God predestinated Calvin to write the Institutes, and if God has predestinated me to write this greatly inferior booklet, it was nonetheless Calvin and it is nonetheless I who must put down the words on paper. Mrs. Smith’s statement, “Either we must do it ourselves, or someone must do it for us,” is in its context a false disjunction. Both Calvin and God did the Institutes. And in an even stricter sense both God and Moses wrote the Pentateuch. They cooperated, and as in all cooperation their precise activities in producing the result were different. God is the source of our abilities and the effective determiner of how we use them. But it is we ourselves who must fight the good fight and run the straight race through God’s grace.