Villa signed off for the season with a 2-2 draw at Wigan Athletic.
Lambert said: "It's been really hard. Especially in that Christmas period when we couldn't get a win. But the big thing was the crowd stayed with it. I think that was a very telling factor.
"Because we were in a transitional period, we knew we had to come through it. I think the club would have kept on sliding. We had to strip it right back and get it going.
"(Chairman) Randy Lerner's been absolutely fantastic with us. He knows the philosophy, that we're trying to build the club. And you see that performance and the performances of the last five months, it's been extremely high."