Christ did not have to offer himself many times. He wasn't like a high priest who goes into the most holy place each year to offer the blood of an animal.
Once a year Aaron must purify the altar by smearing on its four corners the blood of an animal sacrificed for sin, and this practice must always be followed. The altar is sacred because it is dedicated to me.
Then Christ went once for all into the most holy place and freed us from sin forever. He did this by offering his own blood instead of the blood of goats and bulls.
But Christ was sinless, and he offered himself as an eternal and spiritual sacrifice to God. That's why his blood is much more powerful and makes our consciences clear. Now we can serve the living God and no longer do things that lead to death.
If he had offered himself every year, he would have suffered many times since the creation of the world. But instead, near the end of time he offered himself once and for all, so that he could be a sacrifice that does away with sin.
However, only the high priest could go into the second part of the tent, and he went in only once a year. Each time he carried blood to offer for his sins and for any sins that the people had committed without meaning to.