Gatland, who will coach the Lions forwards in South Africa this summer, needs to see his side beat Ireland to hold onto the Triple Crown and beat them by more than 13 points to retain the Championship.
As for Brian O'Driscoll's Irish side, they are a draw or win away from taking the title for the first time since 1985 and a victory away from their first Grand Slam in 61 years.
The stakes are high for both sides, but Gatland has raised them even higher by throwing Lions selection into the equation.
"It is a Triple Crown match, the Irish are coming for a Grand Slam and the championship is up fro grabs as well," said Gatland, whose much-changed side squeezed a 20-15 win over Italy in Rome at the weekend.
"But for many of the players it is going to be a final trial for the Lions, so there is a huge amount at stake in the game."
There are many fascinating duels to be fought all over the pitch and Lions head coach Ian McGeechan is bound to be an interested spectator.
Here are a few of the key individual contests:
Full back: Lee Byrne v Rob Kearney
Wing: Shane Williams v Luke Fitzgerald
Outside-half: Stephen Jones / James Hook v Ronan O'Gara
Second row: Alun Wyn Jones v Paul O'Connell
Back row: Ryan Jones v Stephen Ferris, Andy Powell v Jamie Heaslip and Martyn Williams v David Wallace.
The last time Wales beat Ireland by 13 points or more was in 1983 when the man who will be commentating on the game for BBC, Eddie Butler, led Wales to a 23-9 triumph.
Having made 10 changes to his side for the trip to Rome, Gatland saw his team take a mere five-point victory away with them to set themselves a massive task at the Millennium Stadium on Saturday to hold onto their RBS Six Nations crown.
"The performance was mixed and it answered a few questions, but I'm happy to have come to Rome and got a result. We are still playing for the Triple Crown," said Gatland, who coached Ireland before heading to Wales.
As for the Irish, their so-called 'Golden Generation' is one win away from ending that 61-year quest for a second Grand Slam. They arrived in Cardiff in 1969 hoping to make it four out of four in the then Five Nations, but went down to a 24-11 defeat.
When they arrived at the Millennium Stadium in 2005 it was Wales who were chasing a first Grand Slam in 27 years, while O'Driscoll's men were hoping to hold onto the Triple Crown and take the title.
Wales ran out 32-20 winners on that occasion and many of the same players from that game will be in the thick of the action again this weekend for what is going to be a massive match.
"I won't be shielding the players from the pressure. This is a week to be enjoyed. If you don't enjoy times like this then you won't enjoy anything," said Irish coach Declan Kidney.
"Wales will be tough. They are the defending Grand Slam champions and they're playing at home.
"They are playing for the Championship, the Triple Crown and have rested most of their players this week".