The Dane made a poor error in the Champions League last-16 loss to the Blaugrana last season.
The Blues will face Eintracht Frankfurt in the Europa League semi-finals on Thursday, and Luiz says Christensen will be ready to perform.
Luiz toldStandard Sport: "Andreas is a great player, a great boy. I like the way he thinks about football and looks to play the game.
"People always seem to want to remember what they want to remember, we can't do anything about that.
"What happened to Andreas against Barcelona is in the past and people shouldn't talk about it. It is not nice to talk about it. Chelsea lost against Barcelona, it wasn't Andreas losing against Barcelona.
"Have I tried to help him since what happened last year? Yes. He is a great friend and he listens a lot. We always help each other.
"He has a lot of quality when he has the ball at his feet on the pitch. He is good at reading the game, he is an intelligent and clever defender."