Excellent question.
There is no logical reason for it. Any loving father will pardon the “misdeeds” of his children, without picking out the “most innocent one” and brutally murder him. This whole sacrifice idea was just a leftover from all the primitive religions, where the vengeful and cruel deity had to be appeased by something very valuable.
As the bible says: “the smell of the burnt offering is pleasing to the nostrils of the lord”.
The Jewish sacrificial system was very intricate and was given to the Jewish people by God himself. There was the Burnt Offering, the Sin Offering, The Guilt Offering, the Fellowship Offering, etc. Each different rite had specific rituals for a specific purpose. And each purpose points to a future fulfillment in Christ.
As the New Testament says in Romans, “The wages of sin is death”. This is because a Holy God, because he is holy–not vengeful–can only dwell in the presence of purity, and only those who have been purified can dwell in his presence.
God allowed the Jewish people, through confession and the laying on of hands, to “transfer their sin” onto that of an animal. The animal would then be sacrificed and pay the price of death in place of the sinner.
When we believe in Jesus, confess our sins, and live a holy life accordingly, the death of our Sacrificial Lord takes our place, and through him, we can be admitted into heaven to live in God’s presence.
Either Jesus had to die, or the sacrificial system would have to remain until today. We have sinned, we are guilty, and as the scripture says, “It is the blood that makes atonement, and I have given it to you upon the altar to make atonement for your sins, for it is the blood which makes atonement.” Without this atonement, we would never, on our own, be able to live eternally with God.
Yes, the smell of the burn offering is pleasant to God. It is not because it was a pleasant odor. It is because the Burnt Offering restored the fellowship between man and God. And God loves us so much, that he craves our fellowship–this is his greatest desire–that those whom he created would love him back and enjoy being in his presence, as he enjoys our presence when we spend time with him.