Apologies for the delay in replying @CeciledeVolangesdeNouveau. This is a long post but only really scratches the surface in answer to such huge questions.
You're understandably looking at this from the incredibly narrow perspective of a human. Ultimately we can't even begin to fathom the mystery of why Jesus' death on the cross was necessary - not in this life at least. I don't think we need to understand the reasons behind it either, only to trust and accept that it was necessary.
I find it helps if we think of God as a perfect and holy judge. Imagine you have committed a heinous crime. You couldn't stand before a court of law and say “I’m really sorry for what I did, please forgive me!”. The judge is not going to let you get away scot-free because you have broken the law and the law dictates that justice must be served. You would still have to face the just penalty for your actions.
We all stand guilty before God, humanity being incapable of keeping His law. As it says in Romans 16:23, “For the wages of sin is death, BUT the gift of God is eternal life in Christ Jesus our Lord.”
The natural consequence of turning our backs on God - the very source of all life - is death. Sin (meaning any behaviour which violates the will of God) separates us from having a full and loving relationship with Him. Evil must be punished. However, God, in His love and mercy, gave us a way out and chose to enter into the world, ‘take on flesh’ i.e. become a human being and pay the debt we all owe Himself, by dying in our place and ultimately defeating death through His resurrection. It’s as if the same judge, after passing you the death sentence, takes off their black cap, steps down from the bench and walks to the gallows in your place. This wasn’t child sacrifice - it was self sacrifice. Jesus said, “I am the good shepherd; I know my sheep and my sheep know me - just as the Father knows me and I know the Father - and I lay down my life for the sheep. I have other sheep that are not of this sheep pen. I must bring them also. They too will listen to my voice, and there shall be one flock and one shepherd. The reason my Father loves me is that I lay down my life - only to take it up again. No one takes it from me, but I lay it down of my own accord. I have authority to lay it down and authority to take it up again. This command I received from my Father.” (John 10:14-18).
The Apostle Paul sheds further light on God’s great plan to bring us into a right relationship with Him:
"If we are 'out of our mind,' as some say, it is for God; if we are in our right mind, it is for you. For Christ’s love compels us, because we are convinced that one died for all, and therefore all died. And he died for all, that those who live should no longer live for themselves but for him who died for them and was raised again. So from now on we regard no one from a worldly point of view. Though we once regarded Christ in this way, we do so no longer. Therefore, if anyone is in Christ, the new creation has come: The old has gone, the new is here! All this is from God, who reconciled us to himself through Christ and gave us the ministry of reconciliation: that God was reconciling the world to himself in Christ, not counting people’s sins against them. And he has committed to us the message of reconciliation. We are therefore Christ’s ambassadors, as though God were making his appeal through us. We implore you on Christ’s behalf: Be reconciled to God. God made him who had no sin to be sin for us, so that in him we might become the righteousness of God." (2 Corinthians 5:13-21).
It’s no coincidence that the crucifixion happened during the celebration of Passover - one of the most important dates in the Jewish calendar. Passover was the time when God freed the Israelites from slavery in Egypt. Every household was ordered to slaughter a lamb and mark their doorposts with the blood so that they would be spared from death. Jesus became the sacrificial 'Lamb of God' for all people, for all time; "For you know that it was not with perishable things such as silver or gold that you were redeemed from the empty way of life handed down to you from your ancestors, but with the precious blood of Christ, a lamb without blemish or defect. He was chosen before the creation of the world, but was revealed in these last times for your sake. Through him you believe in God, who raised him from the dead and glorified him, and so your faith and hope are in God." (1 Peter 1:18-21). The whole sacrificial system of the Old Testament was a foreshadowing of Jesus' sacrifice but, as we read in Hebrews, "The law is only a shadow of the good things that are coming - not the realities themselves. For this reason it can never, by the same sacrifices repeated endlessly year after year, make perfect those who draw near to worship. Otherwise, would they not have stopped being offered? For the worshipers would have been cleansed once for all, and would no longer have felt guilty for their sins. But those sacrifices are an annual reminder of sins. It is impossible for the blood of bulls and goats to take away sins." (Hebrews 10:1-3). Why blood? There is a clue in the book of Leviticus when God commands the Israelites not to consume blood; "For the life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar; it is the blood that makes atonement for one’s life." (Leviticus 17:11).
The story of Abraham and Isaac, that you mentioned, also contains a hidden message regarding the crucifixion. In Genesis 22, verse 8, Abraham says, "God himself will provide the lamb for the burnt offering, my son." and in verse 13 and 14 it reads, "Abraham looked up and there in a thicket he saw a ram caught by its horns. He went over and took the ram and sacrificed it as a burnt offering instead of his son. So Abraham called that place The Lord Will Provide. And to this day it is said, “On the mountain of the Lord it will be provided.”
The mountain where Abraham almost sacrificed Isaac was called Mount Moriah which also happens to be the place most scholars agree is the exact location where Jesus was crucified (later known as Golgotha). We see that God did indeed provide the Lamb, as He had promised. At the moment Jesus died, just after He had cried out "It is finished!", an earthquake ripped Jerusalem's holy temple curtain in two. The curtain (or veil) separated the rest of the temple from the earthly dwelling place of God - the 'Holy of Holies'. Only one man - the high priest - was allowed to enter behind this once a year, after much ritual cleansing to make atonement for the people's sins. The destruction of this veil symbolised the ending of the old covenant and the beginning of the new and that Jesus' blood shed on the cross was sufficient for the atonement of sins. We are all now able to enter into the 'Holy of Holies' and have access to God, through Jesus Christ.