If God is perfect, and humans far from perfect, then life would seem to be a constant and unachievable struggle to attain the level of perfection demanded by a holy God. In Old Testament times, human imperfections, sins, were paid for by death, the death of a valuable animal in substitution for the human who had committed the sins. Jesus brought a new way of paying for sins, as chapter 9 of the letter to the Hebrews reveals:
He did not have to offer himself repeatedly, as the high priest enters into the holy place every year with blood that is not his own; otherwise he would have had to suffer many times since the creation of the world. He came once, at the end of the ages, to cancel sin by the sacrifice of himself. Humans are destined to die once, and then face judgment. Likewise Christ was offered once to bear the sins of many, and will appear a second time, not to deal with sin, but to bring salvation to people who are waiting for him.
The old way of making up for sins always left a balance of sins that were unpaid for, and new sacrifices continually had to be offered to pay for new sins. Under the new way brought by Jesus, the sacrifice of himself was sufficient to pay for all sins, whether they had been committed before or after his sacrifice. That is why it is only through trusting in Jesus and his sacrifice that humans can be put right with God.