The Jambos take on St Mirren in the Hampden decider with a squad packed full of talented teenagers.
Barr said: "I don't know if the young boys know how much this is going to mean to them and mean to people for years to come. We all want to win and you need to appreciate the day. But you also have to play the game. You can't get caught up with everything going on around you. You need to go out and win the game first."
The likes of Callum Tapping, Jamie Walker and Jason Holt have all been given important roles to play this season following the departures of established first-team regulars such as Andy Driver and Ryan McGowan.
Barr believes the young players have merited their selection and has told them to enjoy their big day at the National Stadium.
However, he has warned them not to let the occasion get in the way of winning the club's second successive trophy after last year's famous 5-1 win over Hibernian in the William Hill Scottish Cup final.
He added: "Even with everything going on around the club here, you can't think about that. You just have to play the game.
"I don't really think my role as an older player is more important with all the young lads. If you are good enough, you are old enough to play in the first team.
"In games recently, we have seen that there are good young boys here. Maybe the results haven't been great but you can see that the progress is there."
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