It has been suggested that Moses clearly explained why Jesus had to die and that the animal sacrifices symbolized Jesus' death. Do you know where in Bible Moses explained these two things?

And the LORD said unto Moses, Make thee a fiery serpent, and set it upon a pole: and it shall come to pass, that every one that is bitten, when he looketh upon it, shall live. (Numbers 21:8, KJV)

And Moses made a serpent of brass, and put it upon a pole, and it came to pass, that if a serpent had bitten any man, when he beheld the serpent of brass, he lived. (Numbers 21:9, KJV)

Here was ground with which Nicodemus was familiar. The symbol of the uplifted serpent made plain to him the Saviour's mission. When the people of Israel were dying from the sting of the fiery serpents, God directed Moses to make a serpent of brass, and place it on high in the midst of the congregation. Then the word was sounded throughout the encampment that all who would look upon the serpent should live. The people well knew that in itself the serpent had no power to help them. It was a symbol of Christ. As the image made in the likeness of the destroying serpents was lifted up for their healing, so One made "in the likeness of sinful flesh" was to be their Redeemer. Rom. 8:3. Many of the Israelites regarded the sacrificial service as having in itself virtue to set them free from sin. God desired to teach them that it had no more value than that serpent of brass. It was to lead their minds to the Saviour. Whether for the healing of their wounds or the pardon of their sins, they could do nothing for themselves but show their faith in the Gift of God. They were to look and live. {DA 174.4} [The Desire of Ages (1898)]

The sacrificial system, committed to Adam, was also perverted by his descendants. Superstition, idolatry, cruelty, and licentiousness corrupted the simple and significant service that God had appointed. Through long intercourse with idolaters the people of Israel had mingled many heathen customs with their worship; therefore the Lord gave them at Sinai definite instruction concerning the sacrificial service. After the completion of the tabernacle He communicated with Moses from the cloud of glory above the mercy seat, and gave him full directions concerning the system of offerings and the forms of worship to be maintained in the sanctuary. The ceremonial law was thus given to Moses, and by him written in a book. But the law of Ten Commandments spoken from Sinai had been written by God Himself on the tables of stone, and was sacredly preserved in the ark. {PP 364.3} [Patriarchs and Prophets (1890)]

In all these revelations of the divine presence the glory of God was manifested through Christ. Not alone at the Saviour's advent, but through all the ages after the Fall and the promise of redemption, "God was in Christ, reconciling the world unto Himself." 2 Corinthians 5:19. Christ was the foundation and center of the sacrificial system in both the patriarchal and the Jewish age. Since the sin of our first parents there has been no direct communication between God and man. The Father has given the world into the hands of Christ, that through His mediatorial work He may redeem man and vindicate the authority and holiness of the law of God. All the communion between heaven and the fallen race has been through Christ. It was the Son of God that gave to our first parents the promise of redemption. It was He who revealed Himself to the patriarchs. Adam, Noah, Abraham, Isaac, Jacob, and Moses understood the gospel. They looked for salvation through man's Substitute and Surety. These holy men of old held communion with the Saviour who was to come to our world in human flesh; and some of them talked with Christ and heavenly angels face to face. {PP 366.1}
[Patriarchs and Prophets (1890)]