It's not what the atmosphere will do to Barca, it's what it will do to Celtic.
I know that, as a player, it gave me belief I could beat anyone who stood in front of me, even when we were given no chance because the opposition was considered to be far superior.
The perfect example was when we played Leeds United in the semi-final of the European Cup in 1970. There was so much interest in this game that it was switched to Hampden to accommodate the 136,505 who wanted to be there.
It didn't matter it was not at Celtic Park, it was still played in front of the Celtic fans, and the special atmosphere was simply transferred a few miles along the road.
Even when Billy Bremner put Leeds ahead early on, the crowd stayed with us and lifted us to a terrific victory. I am sure the current Celtic players will tell you they get the same boost when these big European nights come along.
The night last November, when the clubs came together to celebrate Celtic's 125th anniversary, was a very special moment in our history, and, as ever, the fans were a very big part of it.
Of course, the downside is that the Barcelona players will now know what to expect and should be better prepared to deal with it. And, in some ways, it will be even harder for Celtic to defy the odds to win again - they are 8-1 for a reason - even with Lionel Messi missing from the Spanish team.
While it is no doubt an advantage to Celtic he is injured, I am sure there will be plenty of supporters sorry he won't be there because how often do you get the chance to see the best player in the world?
For players, that's what playing at this level is all about, testing yourself against the very best. But, even without Messi, Barcelona are still a top, top side, and tonight the mantle of being their catalyst will fall to Neymar.
He's a young man and will be experiencing Celtic Park for the first time. But, exceptional players rise to the big occasion, and he looks every penny the £50million Barcelona paid for him.
He will have been left in no doubt by his team-mates they want to make amends for last year's defeat. That night, they were expecting to book their place in the last 16, but Celtic made them wait - and great teams don't like losing to anyone.
This time, the clubs are meeting much earlier in the group, but it still means an awful lot to both. Barcelona will be wary of what AC Milan might do in Amsterdam against Ajax, and will not want to lose ground in the race to be top of the group.
Celtic will be desperate to avoid having no points from their opening two games as it would add significantly to the pressure going into the double-header against Ajax.
They showed what they were made of with their performance to overcome the 2-0 deficit from the first leg of their play off against Shakhter Karagandy.
But Neil Lennon will want his players to avoid a repeat of the performance against Juventus on the last occasion a really top side played at Celtic Park. They gave it away early that night with the way they defended, and this allowed Juve to flatten the crowd.
Tonight, they have to avoid this happening at all costs.
Everyone in the team has to be on the very top of their form, but, in midfield in particular, they have got to compete. It is not just what Celtic do when Barca have the ball, but what they do when they get it off them.
Any chance to get at what is a makeshift defence must be exploited. It's going to be tough, but past results show there is generally very little between the teams.
And, even without Messi, I would take a point right now.