Towards the end of the Gospel of Luke, we see the torture, death, and burial of Christ. For the disciples, it was over. The man they thought was the Messiah was dead. But then Jesus resurrects and begins appearing to people, walking down roads, chatting with travelers, and showing up at dinner parties.
When the disciples heard the story about Jesus being alive they dismissed it as “an idle tale.” Somewhere between His arrest and death, the true believers became skeptics. And even when Jesus appeared to them, they still didn't understand. This wasn't a second–hand account; the disciples were in the room with the risen Son Of God. And they doubted. Jesus invites them to “see my hands and my feet…touch me, and see” and they still doubted. After three years of following Jesus, when He fulfills His mission to die for our sins and three days later He comes back to life, His closest followers don't even have the faith to believe it.
How much more do we struggle with our own doubts? We can't see Jesus. We can't touch Him. He's probably not appearing to you in your kitchen, asking you to make Him a plate of fish sticks. So we seek Him where He's found—in His word. But we need more than just knowledge. The knowledge of God without revelation from God is incomplete; it's ignorance parading around as wisdom. The Bible is a supernatural book and we need supernatural means to comprehend it. Someone has to “[open our] minds to understand the Scriptures” like Jesus did for His disciples. We can't do it on our own.
In the same way that we're powerless to reconcile ourselves to the Father without Jesus, we're powerless to fully understand the scriptures without the Holy Spirit. Without His help, we can't overcome our own limited understanding. Like the disciples, we miss it. But God graciously gives believers the Holy Spirit to guide us in wisdom and truth so that we can comprehend His word and have strength and encouragement to apply it.
God knows we're too weak to save ourselves and too limited to understand His revealed character and purposes in the Bible. So He sent His Son and His Spirit to stand in our place and do what we can't. God gives us Himself so that we can know and understand Him—not just human knowledge, but divine revelation.