Here’s a helpful post by Jon Bloom from the DG blog. Jon raises an interesting question:
God gave very detailed instructions to Moses regarding the construction of the tabernacle and the keeping of the law. So isn’t it interesting that God didn’t tell Moses how to perform his role as judge in Israel?
Instead he allowed Moses to struggle with an overbearing workload for awhile and then sent Jethro, Moses’ father-in-law and priest of Midian (a pagan priest?), to give him counsel. In Exodus 18, Jethro observes Moses’ administrative approach to judgment and then gives sage advice on delegation. The outcome was a much more effective and efficient way of serving the people.
Why didn’t God just tell Moses that from the beginning?
For one possible answer, read the whole thing.