The gospel, as we know it, is essentially this; that through Christ's death and resurrection we have salvation from sins. And this is so because Jesus Christ was both God and man; He is the incarnation of God Himself. So when we come to the gospels, we can begin to wonder why Jesus didn't appear to teach precisely these things adamantly. Now, I believe that Jesus did teach these things; but even I must confess that these things are not as overt as we might have expected. The evidence that these things are not terribly overt in Jesus’ teaching is the significant number of people who seriously think that Jesus taught a different gospel than Paul (that He taught a "gospel of works") and the number of people who think that Jesus never claimed to be the incarnation of God Himself.
In Matthew 16 we read this:
He said to them, "But who do you say that I am?" Simon Peter replied, "You are the Christ, the Son of the living God." And Jesus answered him, "Blessed are you, Simon Bar-Jonah! For flesh and blood has not revealed this to you, but my Father who is in heaven." (Matthew 16:165-17)
So here we have it; Jesus clearly teaches, by affirming Peter's answer, that He is the "Christ", and Peter understands this to mean that He is "the Son of the living God." Now what did these terms "Christ" and "Son of the living God" mean to Peter and the people of that time? This term "Son of God" certainly did seem to mean to them that Jesus was claiming to be God Himself. In John we read: "This was why the Jews were seeking all the more to kill him, because not only was he breaking the Sabbath, but he was even calling God his own Father, making himself equal with God." (John 5:18). But what about this term "Christ"? What did that mean to them back then?
In those days, the Jews were awaiting the "Messiah", of which the Old Testament prophets had prophesied that God would send. The word "Christ" is the Greek word for "Messiah". They are the exact same word in two different languages; Hebrew and Greek. Now in the Old Testament, King David was called a "Messiah". It means "anointed", but what it meant to people was a King who was sent by God and who would deliver them from their enemies. In the time of Christ, Israel's enemy was Rome. Israel was in Roman hands and the Jews wanted independence from Rome. So they were waiting for this new King to rise up in Israel, who would lead a rebellion to free them from Roman occupation. This is what the term "Christ" meant to people. Now if you ask people today what the term "Christ" means to them, they will probably tell you about Jesus... how He is the Son of God, and how He died and rose again to save us from our sins. We have a very different meaning for the term "Christ". But Jesus was the Christ because, whilst King David was a king who delivered Israel from their foreign enemies, Jesus is the "Spiritual King" of the "Kingdom of God", who delivers us from our Spiritual enemies; namely sin and death.
So going back to that Matthew 16 passage, where Peter had acknowledged that Jesus is the Christ and the Son of God, it says in verse 20, "Then he strictly charged the disciples to tell no one that he was the Christ." This is precisely the kind of verse that bothers many people. They call it the "Messianic Secret". Why would Jesus not want the very essence of the gospel taught to people? Some say He feared being killed by the Pharisees before His ministry was complete, but I doubt this is true. Earlier, at the very beginning of His ministry, they had tried to kill Him but He simply “passed through their midst” (Luke 4:28-30). Nothing would happen to Jesus before God’s appointed time; God is sovereign over all. But perhaps, since we now understand what that term Christ meant to people back then, we can see why Jesus forbade His disciples from teaching that He was the Christ. Jesus did not come to deliver Israel from the Romans; He was not that kind of Messiah. People were too stuck in that expectation that only after Jesus’ death and resurrection would they understand what kind of “Christ” He was. It's doubtful that Peter himself understood, but it was certain that the general public would have misunderstood. Until Christ had died and risen again, a proper understanding of His message and purpose would have been impossible. In verse 21, the very next verse after Jesus had told them not to tell anyone He was the Christ, we read: "From that time Jesus began to show his disciples that he must go to Jerusalem and suffer many things from the elders and chief priests and scribes, and be killed, and on the third day be raised." See there that phrase “From that time...”. In other words, Jesus had not taught His death and resurrection to His disciples at all up until now. Yet this is another of those central points of the gospel. And we see Peter's first reaction to this teaching...
And Peter took him aside and began to rebuke him, saying, "Far be it from you, Lord! This shall never happen to you." But he turned and said to Peter, "Get behind me, Satan! You are a hindrance to me. For you are not setting your mind on the things of God, but on the things of man." (Matthew 16:22-23)
Peter did not understand. Perhaps he's still thinking in terms of a deliverer who would set Israel free from Roman rule. How could such a deliverer be killed? Thinking this way, Peter's mind was on "the things of man", rather than seeing Jesus as a Spiritual deliverer; a “Spiritual Christ”. If Jesus was not able to teach His disciples about His death and resurrection, even after they had just acknowledged Him as the "Son of God", how much more difficult would it have been to make this part of His teaching focus to the masses? Perhaps we can now see why Jesus' message of the gospel, as we see it throughout the four gospels, was not as overt as we might expect. Living on "this side of the cross", we are able to understand who Jesus was and what His purpose was. It's only in light of the cross that we get the right perspective. Jesus had to "ease" His disciples into this understanding only after this point in His ministry. But we cannot deny that Jesus did teach these essential points of the gospel. We understand, for example, what Jesus means when He says “Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. Whoever feeds on my flesh and drinks my blood has eternal life, and I will raise him up on the last day.” (John 6:53-54). When Jesus said these words, many did leave Him because they didn’t understand. But it’s one thing for Jesus to say these hard-to-understand things of Himself, it’s a different thing for His disciples to have said them at a time when they themselves did not understand. Later those disciples would explain Jesus’ ministry. But prior to Jesus’ death and resurrection, they were not to teach but to learn. Now, at Jesus' trial, when it is the final hour, Jesus is absolutely explicit. They ask Him if He's the Messiah, and He tells them "I am", but further goes on to explain what kind of Messiah He is; not the kind they expected, but the kind referred to in the Old Testament book of Daniel...
Again the high priest asked him, “Are you the Christ, the Son of the Blessed?” And Jesus said, “I am, and you will see the Son of Man seated at the right hand of Power, and coming with the clouds of heaven.” And the high priest tore his garments and said, “What further witnesses do we need? You have heard his blasphemy. What is your decision?” And they all condemned him as deserving death. (Mark 14:61-64)