The Obi-Wan Kenobi TV show sheds some light on this. Obi-Wan had originally had some sort of agreement with Owen that Luke would be eventually trained:
OBI-WAN: Is he okay?
OWEN: You don't care if he's okay. You care if he's showing.
OBI-WAN: He's my responsibility, Owen.
OWEN: I'm his uncle.
OBI-WAN: We talked about this. When the time comes, he must be trained.
OWEN: Like you trained his father? (beat) Anakin is dead, Ben, and I won't let you make the same mistake twice. So, leave him on the farm with his family, where he belongs.
Obi-Wan Kenobi, "Episode I", via TV Show Transcripts; emphasis added
Owen apparently changes his mind about letting Luke be trained after the Inquisitors come to Tatooine earlier in the same episode to hunt down Jedi.
By the end of the series, Obi-Wan has resolved to trust more in the Force, and to take a more laissez-faire approach with Luke:
OWEN: What are you, uh, doin' here? I thought you were gonna keep your distance.
OBI-WAN: And I will. You know, you were right. He just needs to be a boy. The future will take care of itself. The only protection he needs now, Owen, is you and Beru. Take good care of him.
OWEN: I will.
Obi-Wan Kenobi, "Episode VI", via TV Show Transcripts; emphasis added
So, in other words, Obi-Wan believed that Luke still needed to be trained, but that the correct time to do so would reveal itself. The Force apparently agrees with him, since it's only after this decision that he's able to see the spirit of Qui-Gon Jinn.