Mark uses the device of irony to drive home his point that Jesus is legitimate even though He was not what people thought the messiah was going to be. The Messianic Secret It is never really explained to us, which is why there are so many theories, but I think if we understand Mark's approach (pointing out all the incongruities) and look at the individual incidents, it can help us. So (very briefly)...

[list][*] Mk. 1.15. Jesus preached boldly. No secret here.
[*] Mk. 1.25. Warfare text: Jesus vs. Satan. Jesus exercises public, sovereign authority. No secret here.
[*] 1.32-34: No secret here. Jesus is publicly impressive.
[*] 1.39. Warfare text. Jesus vs. Satan. No secret here.
[*] 1.40-45. Why the "don't tell anyone"? We are given a small clue in v. 45: So many people clamoring for healing He can't do what He came to do. His popularity and the oppressive crowds were becoming a problem. We might ask, "Did Jesus not want to heal?" Sure He did, but He came for reasons other than that—to explain who He was and to teach about the kingdom of God. He doesn’t want to attract the crowds for what He does, but for who He is. The crowdsalways misunderstood, and were fickle. The crowds never came to him for the right reasons. Jesus doesn't trust a faith based on spectacle. The healing was becoming an interference, and probably not particularly working towards bringing people to the kingdom. We also are finding out that all this attention is raising up enemies (chapters 2-3), and Jesus has to temper this movement of popularity (which has no benefit to the kingdom of God) and the resulting problematic isolation and opposition.
[*] 2.1-12. No secret here. Jesus is bold and public.
[*] 3.7-12. He commands specifically the evil spirits from speaking about Him. No surprise. Who would want their endorsement? The demons always tell the truth, but He doesn't want them doing commercials for Him.
[*] 5.18-20. No secret here.
[*] 6.32-44. No secret here.
[*] 6.55-56. No secret here.
[*] 7.31-36. Another "Don't tell anyone" (v. 36). Interesting, the IDENTICAL language here to 1.44 suggests the same potential problems. The healing would hinder His movement and interrupt His ability to teach. Lane writes, "It was apparently Jesus’s intention to remain in the region of the Decapolis for a period of time and he didn’t wish to be regarded as a Hellenistic wonder-worker." You can see that their amazement is that He can heal, not about His identity as the Son of God. This is a problem that needs to be squelched.
[*] 8.8-12. His miracles are increasing the opposition, and the more He does, the more people are against Him (ironically enough). In 8.12 He sighs with apparent frustration and says, "You know what, we're done with this." Even the disciples are not getting it (8.14-21).
[*] 8.26. He tells the healed man, "Don't go into the village." If I could say it this way, His frustration is building. He is becoming "famous" as a wonder-worker, but people aren't getting it that He's the Son of God. So he asks His disciples, "Who do people say that I am?" (8.27). What's the reputation? We find out it's ALL WRONG. "John the Baptist." "Elijah." "A prophet." Sigh. [b]And then comes the only thing the disciples get right in the entire book.[/b] Peter says, "You're the Christ." So why would He tell them to keep THAT a secret? Because the disciples still don't understand and they're going to spread false information! Look at 8.33, immediately following. The Christ has come to suffer and die, but they don't get that, so they're going to spread the wrong message. Sigh. :(
[*] 9.2-10. The Transfiguration! They can tell about this, right? Nope (v. 9). WHY? Because they didn't understand what "rising from the dead" meant (v. 10). He simply cannot afford to have misinformation spread. Ironically, the demons are the only ones who seem to understand who He is and what He has come to do, but He doesn't want their backing, and understandably so.
[*] 9.14-19. The disciples still don't understand. The people don't understand. Jesus keeps teaching the truth, but people are blind to it (9.32). He doesn't want ANY of them being mouthpieces for Him...yet.
[*] 9.33-34. Sigh. The disciples are arguing about which of them is the greatest. Seriously????? Then in 10.37, they want special privileges. Smack my head.
[*] As I mentioned previously, after Jesus's entrance into Jerusalem (Mk. 11.1ff.), the gloves are off. No more secret. It's an intense time of teaching and conflict.
[*] And...the book ends with the disciples not getting it. Smack my head again. (16.8).[/list]

Why does Jesus command his audience not to talk of his miracles?

I read Mark 7:36 today where he healed the deaf man and tells the people not to speak of this event, and obviously that occurs elsewhere too, but I never understand why he doesn't want peole talking of this. Can someone explain what the reasoning is?