Jesus is not a high priest who is unable to empathize with our weaknesses, but one has been tempted in every way, just as we are—yet he did not sin. Since we have flesh and blood, he too shared in our humanity (he came in the likeness of sinful flesh; was made sin for us; shared in our infirmity; was the Son of Man) so that by his death he might break the power of him who holds the power of death—that is, the devil— and free man who all their lives were held in slavery by their fear of death.
This is the Cross. God reconciling mankind to Himself in the person of Jesus Christ, not counting sin against man.
But freeing from the bondage of sin and death (the power of Satan) is only one part, for is appointed man once to die and then the judgment.
God set forth His Son as a Propitiation through His blood (His blood cleanses from all unrighteousness, in Him there is no condemnation and we escape the wrath to come) to be received by faith. The "last Adam" became a life giving Spirit. He is the Life. The guilty man will perish, and we need to die to sin (the guilty man in us must die and be born of the Spirit (although we die yet shall we live). We must put to death the flesh, die with Christ so that we will live in Him.
A lack of faith in man, man not receiving this propitiation by faith, does not nullify the fact the Propitiation has been set forth to be received by faith.