Sarri drafted Willy Caballero into his starting XI after Kepa refused to be substituted in the closing stages of Chelsea's Carabao Cup final defeat to Manchester City.
Sarri said he was trying to send a message to his squad by dropping Kepa that Chelsea are a team and not a collection of individuals.
While standing by his decision to call on Caballero, who did not face a single shot on target but dealt confidently with any balls into his box, Sarri says Kepa will not be out of the side for long.
Asked whether Kepa was still his number one, the Italian told a news conference: "Of course.
"I think it was the right decision [to drop him]. Kepa made a big mistake. He paid [a fine] with the club and then he paid [with his position] with the team.
"Now I think we have to stop. Kepa will be from tomorrow with us.
"I don't know in the next match if he will be on the pitch or not. But in the next one or two, of course.
"We cannot kill him. When you are young you can make mistakes.
"[But] you need to understand very well after every mistake. For me the question is closed."
Chelsea are next in action on Sunday when they travel to Craven Cottage to take on west London rivals Fulham.