Up until Joseph, we haven’t had dreams. This is a unique method of communication for God when it comes to what we’ve seen so far. Most of the time, God has no problem openly telling people what’s going on, usually in-person. Occasionally there have been angels sent, but it’s always been verbal. It’s always been direct. For it to suddenly to become dreams seems weird.
So why? Well, for this we have to look elsewhere. Yes, God could have easily told Joseph, straight out, that he was going to rule over his brothers and even his parents, but a verbal conversation is not going to work in Joseph’s favor down the line. The dream interpretations, however, do.
In fact, the communications must be in dreams in order for Joseph to do his thing. While God has not put much into dream communication, the Egyptians did. It was common for the Egyptians to receive divine communications in dreams. Pharaoh was quite comfortable asking for interpretations of his dreams because that was the usual mode.
To be the one to help Pharaoh, Joseph had to have experience in interpreting dreams, which he did not just with his own dreams, but for those of the baker and the cupbearer as well.
Now, the dream code is really not that complex, so it’s a wonder that Pharaoh’s couldn’t crack it. Healthy cows and crops going bad is pretty easy to predict a famine or some kind of scarcity. The only x factor is the time. Is it weeks, months, or years? Logical deduction says that to be truly significant, a famine would be in years as opposed to weeks or months. For that matter, Jacob instantly knew what Joseph’s dream of the sun, moon, and stars meant, though that could be attributed to Jacob having received inspiration from God.
Makes you wonder if the Egyptian priests really are capable of doing their job, but more on that when we get to Moses (eventually).