The Ireland full-back made his first start in six weeks on Tuesday, albeit a losing one as the Lions' unbeaten Australia tour record ended with a 14-12 defeat against Jake White's Brumbies.
Kearney said: "It was one of the things that we spoke about, that the guys who played (against the Brumbies) have an onus to get back into the mix, It's really important, and probably the biggest thing sometimes when it comes down to these touring sides and there is a big group of 37 guys involved. But the big picture is Saturday."
He added: "That is all that matters, and we have to do everything to make sure that whatever 23 are selected are in the best frame of mind for it."
Few Lions players covered themselves in glory at Canberra Stadium as the Brumbies became Australia's first provincial team conquerors of the tourists since Queensland triumphed 15-11, 42 years ago.
While Lions head coach Warren Gatland's Test team selection - it will be announced in Brisbane on Thursday - appears largely cut and dried, a three-match series means much can change between now and the Sydney finale on July 6.
"This was my first start in six weeks (after injury), so I just wanted to get some time under my belt and put in as best a performance as I could," Kearney said.
"It wasn't really a night for full-backs, but that is the way it goes sometimes.
"You don't get too many chances, but sometimes when you are least expecting a second chance you get it.
"There is one more midweek game to go, and there will be injuries - as we've seen in every game. The attrition rate seems to be pretty high, so a lot of guys will get second chances."