In John 16:25-33, Jesus prepared His disciples for what lay ahead.
"'I have said these things to you in figures of speech. The hour is coming when I will no longer speak to you in figures of speech but will tell you plainly about the Father. In that day you will ask in my name, and I do not say to you that I will ask the Father on your behalf; for the Father himself loves you, because you have loved me and have believed that I came from God. I came from the Father and have come into the world, and now I am leaving the world and going to the Father.' His disciples said, 'Ah, now you are speaking plainly and not using figurative speech! Now we know that you know all things and do not need anyone to question you; this is why we believe that you came from God.' Jesus answered them, 'Do you now believe? Behold, the hour is coming, indeed it has come, when you will be scattered, each to his own home, and will leave me alone. Yet I am not alone, for the Father is with me. I have said these things to you, that in me you may have peace. In the world you will have tribulation. But take heart; I have overcome the world.'"
The point of Jesus's words was to prepare the disciples for their imminent spiritual failure. The most notable was Peter's actions in the Garden of Gethsemane. The guards come to arrest Jesus, and Peter, having a sword, drew it and struck the high priest's servant and cut off his right ear (John 18:10).
Peter was ready to protect Jesus, to fight for his Master. But a few hours later, after the Lord was arrested, Peter swore he didn't even know Him.
How is that possible?
How is it possible that today someone who seems to love Jesus, who ministers in His name, falls into sin?
The life of a Christian begins with repentance (turning away from sin) and faith, but it doesn't end there. Instead, these become our identifying marks. Christians don't repentant and have faith once. They are to mark each day. We fail all the time. Some sins, however, are more apparent than others.
Even King David sinned grievously. He abused his royal power. He took another man's wife for his own—and saw to it that this man died on the front lines. How could David receive the title "a man after God's own heart"?
In Psalm 51, the prophet Nathan confronted David. And what was the king's response? He was devastated when he realized what he had done. David was called a man after God's own heart not because of how religious he was but because of his repentance.
Jesus knew the disciples would desert him. He knew they would sin. He knew they would need understanding and clarity of thought when these things took place.
John 16:25 says, "I have said these things to you in figures of speech. The hour is coming when I will no longer speak to you in figures of speech but will tell you plainly about the Father."
Two phrases pop out, "these things" and "figures of speech." Jesus recognized He'd been saying things that were hard to understand, not only in the upper room but also in the three years He'd been with the disciples. So, He promised them that a time was coming when He would speak about the Father in such a way that they would understand.
In John 2:19, Jesus said, "Destroy this temple, and in three days I will raise it up"
In John 16:21-22, we read, "But he [Jesus] was speaking about the temple of his body. When therefore he was raised from the dead, his disciples remembered that he had said this, and they believed the Scripture and the word that Jesus had spoken."
It wasn't until after Jesus died and rose again that the disciples understood much of what He had taught them. Why not make it clear from the beginning?
If Jesus had done that, our tendency would be to believe we were clever and figured things out on our own.
Charles Spurgeon once said, "If we have to put one stitch into the garment of our salvation, we shall ruin the whole thing." 
God knows how much insight and understanding we can process at any given time and reveals the truth accordingly.
Think of a child. It doesn't matter how much time you spend trying to explain a concept to them. If they're not mature enough to grasp it, it won't matter what you say or do. The Lord works the same way with us. He's our patient Father, understanding exactly where we are in our development. He understands exactly how much we're able to learn and how best to teach us. He gradually instructs us based on what we can handle. And one of the tools God uses for us to grow spiritually, to learn more about Him, is our spiritual failure.
The only true happiness anyone can experience is having a deepening relationship with Jesus. And since God uses our spiritual failures for our growth, we can find encouragement and comfort, knowing that, in the end, it truly is for our good.
 Sermon #91 "Christ Exalted" Sunday evening July 6, 1856 at New Park Street Chapel, Southwark (pronounced "Suthick"), London. Scripture Hebrews 10:12-13