This is what happened to Peter with the Gentiles. Peter had his dream about the sheet coming down from the sky filled with all kinds of creatures (clean and unclean) which led to him going to a Gentile's house where the entire household accepted Christ. When he was relating this story to Jewish believers he said, 'And as I began to speak, the Holy Spirit fell upon them, just as He did upon us at the beginning. And I remembered the word of the Lord, how He used to say, "John baptized with water, but you shall be baptized with the Holy Spirit."'" Acts 11:15-16
Peter didn't get it until this occurance! He didn't get that the Holy Spirit was not just for Jews but also Gentiles until these words of Jesus from the past came back into Peter's mind.
This is how it often works with us. We go through life dealing with whatever comes. Sometimes we might do it mindlessly. But even when we aren't aware of it God is working. And when He needs to use what He taught us He will bring it to mind at just the right time. And we will think, "Oh! That's what God meant!!"