Bent was left out of the squad for Villa's draw at Arsenal on Saturday.
Lambert said: "That's my decision. I'm the man that picks the team.
"Listen, it's my choice and I've 26, 27 lads that I have to look after. Everybody's in it together and I need everybody in it together.
"I know the disappointment when you don't play. I was dropped about five million times as a player, but that's the nature of the game.
"If you could pick everybody you would. Darren's still part of it but I've got 25, 26 guys to take care of and think of."
Lambert reiterated that there is no rift with Bent but did not say whether he will be involved in some capacity for Tuesday's home game with Reading.
He said: "Darren is fine. There's nothing at all. The most important thing is Aston Villa Football Club."