Edwards said there had been an incident the week before with another man who had a gun, so he was carrying the knife for protection, although he hadn't planned to take it into the central city with him.
"It was just a spur of the moment thing, let's go to town, okay," he said.
But why he stabbed Soper remains a mystery - Edwards was unable to explain to Judge Hobbs the motivation behind the attack.
"I can't justify it," he said.
"I was in a state at the time . . . I misread the situation."
He said it was a case of "wrong place, wrong time".
Edwards and Soper do not know each other.
Soper is the son of Newstalk ZB's political editor Barry Soper.
Barry Soper has previously spoken to the Herald about the shock the incident caused, which left his son in hospital and needing surgery.
Judge Hobbs referred to a similar case in which a bouncer asked a man to leave a bar, and the man then grabbed him and shoved a screwdriver into his neck. In that case, the victim was fortunate to only suffer a small puncture wound to his throat.
He said Soper's injuries were more serious.
He remanded Edwards on bail to July 27 for sentencing, to give him time to make a reparation payment for Soper. This would be considered a mitigating factor, he said.
