Why did Obi Wan wait three years

[Darth Yan]

Empire Strikes Back takes place 3 years after A new hope. Why would Obi Wan wait all that time to tell Obi Wan to meet Yoda? Seems unusual .

[Lord Revan]

It's possible that Obi-Wan didn't wait but those 3 years were due to luke not really being strong enough to hear him expect in Battle of Yavin, in essense Obi-wan was constantly sending the "seek out Yoda" message to Luke but it wasn't until Hoth that Luke was able to hear it. Note that it's until close to the end of Luke's training with Yoda that he's able to communicate with Obi-Wan's spirit directly rather then just getting a Force vision version of a "pre-recorded" message.

[Darth Yan]

Luke was never weak. He had a lot of potential in the force.

[bilateralrope]

Maybe Obi-Wan had to spend some time gathering his strength until he was able to send the message.

[Q99]

Luke picked up the message when he was weak- maybe he had to lower his mental defenses.

[Adam Reynolds]

Luke may have been physically weak in the sense that he was injured, but that may have been the first time he fully used the Force since the events of ANH, strengthening his connection. I am sure the EU contradicts this, but it is the only good explanation I can think of.

[Lord Revan]

Luke was never weak. He had a lot of potential in the force.

I meant weak as in "not yet able to use most of that potential", in essense it could be that before that point Luke was not "trained" enough to pick up the message and as others have pointed out he was physically weak at that point so he might have been drawing from the Force to survive either intentionally or unintentionally.

[Abacus]

Raw potential does mean accessibility. If you recall, Luke only received the message after having delved deeper into the Force in order to help himself escape the wampa. It's not that hard to make the connection that, in order to "hear" the message, Luke first had to make a stronger connection with the Force. It is also significant that he was perhaps not ready yet to begin further training.

And if potential was enough, then Anakin Skywalker would never have needed training from Obi-wan Kenobi in the first place and there'd be no younglings in the Jedi Order; people would just wake up and go, "Oh yeah, I've got that Force thing. Guess it's time to start doing Force stuff."

[Lord Revan]

It's essentially like this, the Force potential is like the max bandwith the cables to your device, while the connection with the Force is like the bandwith of your network connection (be that the internet or some other network), the network connection cannot ever exceed the bandwith of the cables but can be much, much lower. Same idea with one's connection with the Force you can have great potential but unless you've trained to connect with the Force your actually connection will be weak.

[Q99]

Luke finally got good enough Ping for Obi-wan to connect.

[Gandalf]

Luke was never weak. He had a lot of potential in the force.

A lot of people have all sorts of potential, from intellectual, physical and all sorts of things. Potential needs to be nurtured through training. That's why gifted children still go to schools and gifted athletes still train every day. Potential strength must be turned into actual strength. There aren't a lot of people who are at the top of their field, and haven't practiced their way there. Luke wasn't there at Yavin. By Hoth he was.