Okay, I'm going to get kind of heavy here. I've been doing a bible study on the book of Hebrews, so I've been reading and thinking on these things for the last few weeks.
Jesus' sacrifice is actually explained in detail in the book of Hebrews. After addressing the superiority of Jesus to Moses, the Aaronic priesthood, and the Old Covenant, and addressing Jesus' suitability as perfect high priest, the author addresses Jesus' superiority as a sacrifice, and the superiority of the new covenant that his sacrifice brings starting in chapter 9. You can read the relevent bits here:
Hebrews 9 and 10, but I'll give a bit of a summary with bits pulled from scripture in italics.
First, the author talks about the old tabernacle. Now, in the days of the Old Covenant, when the Jews still offered sacrifices in the tabernacle. The most holy place in the tabernacle was called, appropriately, the Most Holy Place.
But only the high priest entered the inner room [the Most Holy Place]
, and that only once a year, and never without blood, which he offered for himself and for the sins the people had committed in ignorance. If another person tried to enter the Most Holy Place, or if the high priest wasn't sufficiently holy, God would strike that person dead, because they could not bear His presence and live. When the high priest went in, therefore, they would tie a rope to his ankle, so that if God struck him dead they could pull him back out again. That's how serious this was. And this was only in the earthly tabernacle, where the duties performed were just
external regulations applying until the time of the new order.
Now, when Christ came as our high priest, He didn't enter the earthly tabernacle of the Jews. He entered through the perfect tabernacle of heaven. And just like the tabernacle in heaven is greater than the one on earth, the sacrifice required to enter it is greater than the sacrifice given by the Jewish high priest. The Jewish high priest would enter with a sacrifice of a young bull and goat, which would outwardly cleanse the people of Israel for one year. But Christ entered the tabernacle through the sacrifice of His own blood, which cleanses our hearts forever! The reason that Jesus only sacrificed Himself once is because that is all that is needed. His once for all sacrifice cleanses those who made it.
But why was a sacrifice needed at all? The author of Hebrews compares it to a will. When a will is made, it is only put into effect when the person who made it dies. The Old Covenent was put into effect by the blood of many animals.
In fact, the law requires that nearly everything be cleansed with blood, and without the shedding of blood there is no forgiveness. And so the New Covenant was put into effect by a death, and since it is greater than the Old Covenant, it requires a greater death.
I'll quote 10:11-22 in full, since the author puts it much better than I can. (In fact, the entire passage is written better than I can write, but this bit especially.)
Day after day every priest stands and performs his religious duties; again and again he offers the same sacrifices, which can never take away sins. But when this priest [Jesus]
had offered for all time one sacrifice for sins, he sat down at the right hand of God. Since that time he waits for his enemies to be made his footstool, because by one sacrifice he has made perfect forever those who are being made holy. The Holy Spirit also testifies to us about this. First he says:
"This is the covenant I will make with them
after that time, says the Lord.
I will put my laws in their hearts,
and I will write them on their minds."[g] Then he adds:
"Their sins and lawless acts
I will remember no more."[h]
And where these have been forgiven, there is no longer any sacrifice for sin. Therefore, brothers, since we have confidence to enter the Most Holy Place by the blood of Jesus, by a new and living way opened for us through the curtain, that is, his body, and since we have a great priest over the house of God, let us draw near to God with a sincere heart in full assurance of faith, having our hearts sprinkled to cleanse us from a guilty conscience and having our bodies washed with pure water.
So instead of having a high priest who can only enter the Most Holy Place once a year to sacrifice for our sins, we can enter the Most Holy Place ourselves, whenever we like, because of Jesus' sacrifice. We don't have to always be atoning for our sins, because He has done it for us. The sin issue is basically off the table, and we can communicate with God without being burnt up by His holiness. And if that ain't a major sacrifice, I don't know what is
I know this is a big information dump. If you find any part of it unclear, just tell me, and I'll do my best to explain it better.
, but from what I have heard and understand, God is Jesus... Please make it clear. 
