Question: Isn't it true that humans are so innately sinful that they need an outside sinless agent to redeem them from sin?
Answer:
God says of sin, "you may rule over it" (Genesis 4:7). Yet, "there is no man that does not sin" (1 Kings 8:45). Indeed, "Who can say, 'I have made my heart clean, I am pure from my sin'?" (Proverbs 20:9). That is why God provided Israel with the means of cleansing itself from sin through the sacrificial system, which includes blood offering and repentance. By God's grace, when the system cannot be fully utilized repentance alone suffices (Psalms 69:31-32, 1 Samuel 15:22). The remedy for sin is clear, "But if the wicked turn from all his sins that he has committed, and keep all My statutes, and do that which is lawful and right, he shall surely live, he shall not die" (Ezekiel 18:21). An individual that sins can utilize those statutes that provide for reestablishing a right relationship with God.
According to the Jewish Scriptures, repentance is open to Jew and non-Jew alike (Jonah 3:5-10, Daniel 4:27). The repentant sinner undergoes genuine remorse for his past misdeeds and pledges himself to improve his ways in the future. He is to make every effort to keep away from all past transgressions. However, if righteous acts are done insincerely as an attempt to hide unrepentant iniquities, "all our righteousnesses are as a polluted garment" (Isaiah 64:5).
The Christian concept is that man is hopelessly entrapped in innate original sin. However, the Jewish Scriptures provide ample testimony that although man may have an inclination towards evil (Genesis 8:21) the means of reestablishing a right relationship with God are always at hand for Jew and non-Jew alike through sincere repentance (Psalms 32:5).
There is no innate sin that separates the individual from God and forgiveness of sin is not dependent on a sinless sacrifice. Even when sacrifices were offered in the Temple the sinless animal's blood did not automatically redeem from sin. Blood sacrifice was part of a process that was primarily dependent on confessionary prayer to achieve reconciliation between the repentant sinner and God.