A person who God considers spiritually unacceptable or defiled is spoken of as if the person were physically unclean. (See: [[rc://en/ta/man/jit/figs-metaphor]])
Here the word "keep" means to observe. Alternate translation: "observe the Passover" or "celebrate the Passover" (See: [[rc://en/ta/man/jit/figs-idiom]])