Messi struck a hat-trick in Sunday's victory over Real Zaragoza.
"Put in the superlatives yourselves, I'm running out," Guardiola said. "It's already been a while now that he has been outstanding.
"He's more than decisive in every way.
"That he's capable of doing everything that he does at his age is something impressive, that doesn't make any sense."
Messi was a major doubt before the match as he was suffering from a dental abscess.
And Guardiola admitted it would have been hard to leave him out, with the youngster also desperate to play.
"It wasn't an infection in the tooth, it was in the gum. He was in a lot of pain. But in the morning I asked him how he was and he told me that he was better," added the Barca boss.
"Before the game I asked if he wanted to play and he said yes, I asked him how many minutes and he told me the whole game.
"He always wants to play, whether it's the Champions League final or against a third-division side.
"For me it's difficult to leave him out, seeing the form he's in.
"He's an amateur in this sense, he always wants to play.
"Obviously his game has a great impact on our team. The day he's not there we will respond, knowing that with him we are better. There are others who will take on the responsibility that he is doing."