When man fell by transgression the law was not changed, but a remedial system was established to bring him back to obedience. The promise of a Saviour was given, and sacrificial offerings pointing forward to the death of Christ as the great sin offering were established. But had the law of God never been transgressed, there would have been no of sacrifices...
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 heathen customs with their worship; therefore the Lord gave them at Sinai definite instruction concerning the sacrificial service. (Patriarchs and Prophets, 363, 364)
Reflection: The sanctuary service had become necessary because men had strayed far from God. Man's mind had become so darkened that a simple illustration of the gospel needed to be instituted.