MacArthur isn't the only one, by any stretch.
So is Lordship Salvation biblically valid?
Lordship Salvation promotes a synergistic sanctification, which I, and most solid Reformers reject.
I do not consider MacArthur to be genuinely Reformed; nor do I think he and his ideas reflect the historical Reformed fathers.
A quote from Martin Luther:
“Faith alone justifies, but not the faith that is alone.” “Works,” Luther said, “are not taken into consideration when the ques*tion respects justification. But true faith will no more fail to produce them than the sun can cease to give light.”
Why?
Because of the indwelling Holy Spirit in every regenerated believer.
Sanctification and bearing the fruits of God, are as monergistic as justification, calling, drawing, regenerating, converting, preserving, and bringing the sons to glory in Jesus Christ.