This is a GREAT question and is one of the weak spots of Christianity. But as a Christian, I believe there had to be reason.
If one reads Isaiah 53, it's clear that Jesus was the fulfillment. But when he asked the Father whether the bitter cup could be removed, the answer was invariably no. It shows that the Father 1) either couldn't effect the atonement without the sacrifice of his Son, or 2) the Father didn't want to remove the bitter cup. I believe the answer is (1) the atonement coul not be effected until Jesus took upon himself the sins of the world and died.
If true, that meant that the Father could not have spared Jesus. If Jesus taken upon himself the sins of the world and offered up his life, the atonement could not and would not have taken place.
Does that mean that the Father could not have initiated the atonement without this taking place? Yes. In some way we don't understand, he was bound by a law that required a sacrifice for sin. But how can that be if he is all powerful? Didn't he have the power to forgive Adam's transgrression without a blood sacrifice? I'd like to see a Jehovah's Witness elder answer for that one. In fact, most Christians don't have an answer. All we know is that it was necessary. God operates under certain laws of mercy and justice, and these are laws under which he is bound.
Again, read Isaiah 53. Also Hebrews and I John. We become joint heirs with Christ. As the Son sits upon the throne of his Father, we sit, or inherit, his throne, which is the throne of his Father. Jesus becomes like the Father and we, being joint heirs, become like Jesus and we inherit "ALL that the Father has." The Jehovah's Witnesses kind of live in a world outside that of most Christians in that they believe Jehovah is the Father, not the Son. But in describing his return, in Zechariah, he speaks of the Jews rushing to meet him. And one says unto him, "What are those wounds in thine hands?" And Jehovah replies, "Those which I received in the house of my friends."
Jehovah judges mankind by means of the atonement and it is he who will judge the nations. And yet John states that "the Father judgeth no man, but has committed all judgment unto the Son." (John 5:22) Thus, Jesus is Jehovah. According to many of the apocraphal books, Jesus' atonement covers more than this earth, but many others. How it works out, we don't know. But we know it was something that had to happen. The "bitter cup" could not have been removed, or I think it would have been.
Just me two cents.