"The importance of a Lions Tour, number one, is because of its scarcity. A lot of players go through their long careers and play a lot of Test matches and they don't have the opportunity to play against the British & Irish Lions," said Eales.
"Two years before I started in Test Rugby there was a series in 1989. In my last season of Test Rugby the British & Irish Lions were back in Australia.
"I felt very fortunate to have had the chance to play them. It was motivation at the start for me and at the end, but for very different reasons."
Gregan, the most capped Test player in rugby history with 139 appearances for the Wallabies, echoed Eales' sentiments about the magnitude of a Lions tour.
"You get players knocking lumps out of each other from England, Ireland, Scotland and Wales and then all of a sudden in a short period they come together and play as one. The thing which binds them and brings them together is that Lions jersey," said Gregan.
"It's got a rich history and they get together really quickly and they work really hard for each other. The thing that unites them is that Red jumper, they play for it and history shows that.
"The calibre of this team which is going to come out here next year is going to be fantastic and it's going to set up an epic series."
Former Wallabies fullback Matt Burke, who scored 44 points in the two Test triumphs in 2001, said it was the highlight of any Northern Hemisphere player's career to win a Lions cap.
"It just means so much to those guys if they can get chosen on a Lions Tour, there's just plenty for those guys to play for," Burke said.
"If they can represent the Lions it just puts them on another level, especially when you look back at history and the names who have played in the Red jersey. I guess the closest we would get would be if you were to combine an Australian, New Zealand and South African team - that would be the next pinnacle for Southern Hemisphere Rugby players."