en_tn/1co/05/08.md

not with the old yeast, the yeast of bad behavior and wickedness ... the unleavened bread of sincerity and truth

Paul continues using the proverb from 5:6 to teach his audience. Here "yeast" is a metaphor for sin, and "unleavened bread" is metaphor for behaviors acceptable to God. (See: rc://en/ta/man/jit/figs-metaphor)