Lambert became the Reds' first signing of the summer when he was brought in from Southampton for around £4 million earlier this month.
The deal to land the 32-year-old England international caught many off guard, but Barnes, who starred for the Reds from 1897-1997, thinks that Lambert will prove to be an inspired piece of business.
The former England international told Sports Mole: "[Lambert is] a great signing for Liverpool because what they need is players that can keep the momentum going and keep the quality high - they couldn't do that in the past. Although Luis Suarez missed the first six games, they were rarely without both him and Daniel Sturridge, which is just as well because they couldn't replace them.
"Now, with Lambert and [Emre] Can, the players on the pitch can be replaced with equal quality so the consistent performances can continue. We didn't need that last year because most of the players stayed fit and played well, but that doesn't normally happen and it won't happen this coming season. Someone is bound to lose form or pick up an injury and while they didn't need replacements last season, if they had have needed some, it was in short supply."
Barnes also backed the pursuit of Southampton captain Adam Lallana, after the five-time European Cup winners made a reported £25 million offer for the 26-year-old.
Lallana scored nine goals and contributed six assists for the upwardly mobile Saints last term, and Barnes thinks the England international would be ideal at Anfield.
"Brendan Rodgers is giving British players a chance and Lallana is showing that British players can be just as good as foreign players," he added. "Lallana coming in would be a big plus, but we also need to sign two or three defenders and maybe a defensive midfield player. I'm sure [Rodgers] will do that, although they might have to come from abroad."