"Wherefore when He cometh into the world, He saith, Sacrifice and offering Thou wouldest not, but a body hast Thou prepared me." It then continues with this, negating, it would seem, the whole scheme of animal sacrifice theretofore: "In burnt offerings and sacrifices for sin Thou hast had no pleasure." (Hebrews 10:5-6, emphasis mine)
This idea, that Jesus was the perfect sacrifice, is, I think, largely untouched by modern, mainstream (read: Main street) Christianity. And forgive my ample comma usage, but I don't know how else to say it. When you walk with Him for a while, you begin to feel the ease of His grace at work in your life. There are strictures and strains of self-defeating thought you don't feel anymore as the Holy Spirit intimates to you a way of life more in keeping with Jesus. But did you know, "whosoever shall keep the whole law, and yet offend in one point, he is guilty of all" (James 2:10)? What this means is, that if you endeavor to uphold--and hold up--the sacrificial paradigm, i.e. "doing things for God so as to merit something you never could" as valid, and you slip up in the slightest, you fail the whole course. This is why God had to prepare Jesus a body. Because no one was able to "keep the whole law". And then, assuming you did (not possible, humor me), it would all have been your own works, thus negating the necessity for Jesus at all.
Subrogation, legally speaking, is where a person acts as a go-between between two disputing claimants. For instance, say I owe money to an institution, the act of subrogation by my friend puts him in place of me for paying back the sum I owe. Thank you very much.
"And thou shalt be blessed; for they cannot recompense thee: for thou shalt be recompensed at the resurrection of the just." (Luke 14:14)
That's what Jesus' sacrifice is. A payment on our behalf. This is one of the reasons the Christian is ready to die. Because the whole idea has been raised one higher. To where "the good life" is a misnomer and anything alongside that could be seen, as Paul rightfully wrote, as "dung" (Philippians 3:8). But first, a little more exposition on what Jesus did.
Few, and far between
"For to me to live is Christ, and to die is gain." (Philippians 1:21)
"I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me and gave Himself for me." (Galatians 2:20)
Because of the life Jesus lived--thirty-three short years full of fun and adventure (and it's the latter three we get a window on)--the whole of "life" has been sanctified before God. If you really wanna fill an afternoon (or two, or three), try and line out all of the various penalties incurred due to everything from well-meaning (death--2 Samuel 6:7), to petty larceny (death for the offender and his whole family--Joshua 7:19-26), to something so innocuous as taking a census (plague--2 Samuel 24). The point is, things are serious with God the Father. In order to fully cancel our debt, Jesus had to pay the ultimate price. This is why He would so censure Peter as to rebuke the devil speaking through him when he told Jesus He wouldn't have to--die, that is (see Matthew 16:21-23).