There is much difficulty today in the sharing of the Law’s dispensation and is understandably so, because of the teachings of our upbringing in the knowledge of Christ. I believe the focus on the present dispensation is the life of Christ (Col 3:4), which those prior to the giving of the Law were predisposed of concerning faith, which they (i.e. Abraham, David, etc.) walked in through the revealing of Christ's atonement in types and shadows.
Faith in God has always been within believers in Him, which could not come from the Law. Instead of faith and life, the Law brought condemnation and death by the truth which revealed where man was guilty, and this was one of its purposes (the other being sin's condemnation in Christ's crucifixion) so God could begin teaching and drawing others to Him. The Father sending His Son was the final act concerning faith in those who desire to be right with Him.
It's all about "faith,“ and ”the Law is not of faith," but rather confirmation of judgment in the attributing of guilt: "And the commandment, which was to bring life, I found to bring death" (Gal 3:12; Rom 7:10).
The Law can be nothing but good (Rom 7:12), the instruction is in what the Law incurred (guilt) and even this is good, but only to those who desire to be right with God.
"Was then that which is good made death unto me? God forbid. But sin, that it might appear sin, working death in me by that which is good (Law); that sin by the commandment might become exceeding sinful" (7:13).