And Moses stripped Aaron of his garments and put them on Eleazar his son. And Aaron died there on the top of the mountain. Then Moses and Eleazar came down from the mountain. Numbers 20:28 (ESV)
The priesthood of Aaron prefigures the priesthood of Jesus Christ, although the Priesthood of Jesus replaces and supersedes that of Aaron. One of the key reasons what Jesus has a better priesthood is that he ever lives to make his promise good and intercede for the people unlike the Levitical priesthood that was always limited by death as we see in Aaron’s death (which according to verse 24 was judicial). See Hebrews 7:23-27 for the New Testament reading on this.
And the LORD said to Moses, “Make a fiery serpent and set it on a pole, and everyone who is bitten, when he sees it, shall live.” Numbers 21:8 (ESV)
This prefigures Christ two and is explained best in the words of Jesus himself from John 3:14-15 “And as Moses lifted up the serpent in the wilderness, so must the Son of Man be lifted up, that whoever believes in him may have eternal life.”
But I, brothers, could not address you as spiritual people, but as people of the flesh, as infants in Christ. I fed you with milk, not solid food, for you were not ready for it. And even now you are not yet ready, 1 Corinthians 3:1–2 (ESV)
Paul is calling the Corinthians to maturity in Christ, it is not that he taught them a simplified Gospel, because the Gospel is the deepest and most profound truth in the world. The allusions to infancy, milk and being fleshy is Paul pointing to the immaturity in the hearers of his Gospel message. In them proclaiming themselves to be wise and seeking worldly wisdom, the truth of the Gospel was like milk to them when it is in fact solid food. This happens every week when Sermons are preached at church they are milk or solid food based on the way we hear not the message given. We do not need a change of diet but a change in perspective because the gospel is glorious!
For though you have countless guides in Christ, you do not have many fathers. For I became your father in Christ Jesus through the gospel. 1 Corinthians 4:15 (ESV)
We need to clearly identify and thank God for our fathers in Christ, those who do not just teach but care for our souls… Our Pastors.