Murray, an Irish Under-21 striker, became John's first signing as Argyle manager on Thursday, joining on loan from Ipswich Town until the end of the season.
However, before he had arrived in Plymouth, John was already excited with the 21-year-old's enthusiasm and attitude.
“I'm very pleased to get Ronan in," said John who was given a steer by a former Ipswich manager.
“Paul Jewell was the one who put me on to him and I’ve checked him over and I'm really pleased to get him.
“He's a good intelligent footballer who scores goals and he did well when he went to Swindon last year in a promotion-winning side.
“It's important that he has experience at this level but I found out how much he wants to play.
“Straightway, he wanted to come and that's what I like in a player.
"There were no ifs or buts, he just said: 'I'll be there'.
“I like that and it shows me that he wants to come and play football.
“He's played at a higher level, too, in and around Ipswich who are an excellent Championship club and [Ipswich manager] Mick McCarthy couldn’t speak highly enough of him."
Despite being a long way from home, Ronan will meet a familiar face in Pilgrims' midfielder Conor Hourihane.
Last season, the two young players lined up alongside each other for the Republic of Ireland Under-21s in a friendly at the Estadio Municipal de Agueda which the home side won 2-0 with two late goals.
“It'll help Ronan that he knows Conor," admitted John.
"Maybe it'll make him settle in a little quicker.
“Hopefully he'll hit the ground running on Saturday and give us a lift.”