There are so many sacrifices in the Old Testament. Like…a lot.
To make it simpler, most scholars place them in five different groups: burnt offerings, grain offerings, peace offerings, sin offerings, and trespass offerings. Not all of them are put on the altar and lit on fire; indeed, some are simply placed at the doorway and presented to God (and later eaten by the priests or the offerer themself).
Each one of those types of sacrifices has sub-groups underneath them, though. For instance, Leviticus 1 discusses burnt offerings, but there are several different types of burnt offerings. Depending on the situation, you may offer a bull or a male goat or a bird. Just depends on what you’re hoping to accomplish and what you have available.
The same goes for the priests. Before they could start their priestly service, there needed to be a consecration ceremony, which would necessarily involve some sacrifices. The steps are outlined here in Exodus 29, while the actual service itself would take place in Leviticus 8.
For the ceremony, the priests were to take “one young bull and two rams without blemish,” along with a basket of unleavened bread, cakes, and wafers mixed with oil (Exodus 29:1-2).
Before that though, the priests were to all be washed thoroughly with water (Exodus 29:4).
Purification through water is not a new topic in the ancient world. Most priesthoods of major religions required their priests to wash regularly. Some even did so several times a day.
However, for the Jews, this was the first time in Scripture that water purification is mentioned. In Leviticus 14-15, water was used to cleanse people from ritual defilements, like if they came into contact with a corpse or ate a forbidden animal.
It’s impossible to see this without making a connection to the New Testament practice of baptism. Just like the priests could not begin their service to God until they were washed (Numbers 8:5-13), so we cannot begin our “priestly service” until we’re cleansed (Acts 22:16).
It’s a shame that so many people in our world relegate baptism as being “optional,” when the Text clearly states that all believers are to be baptized (Mark 16:16; Matthew 28:19; Acts 2:38; 1 Peter 3:21). If we’re not cleansed, how can we possibly hope to enter into the service of God?
Aaron never fought these regulations. Leviticus 8 shows him going through every single step outlined in Exodus 29—sacrifices and all. What does it say about our heart when we refuse to follow God’s rules for consecration?