Instead He purged the leaven. Leaven is a figure of sin, particularly sins of pride, because it puffs up. Pride is the kind of sin that undergirds other kinds of sin. If somebody has a greed problem, for example, their underlying problem is pride. If somebody has a lust problem, their underlying problem is pride.
Pride is the sin that underlies other kinds of sin.
Pride is also associated with false doctrine. The Sanhedrin was responsible for the inspection of lambs at Passover. They checked for up to seventy-four different blemishes. If unable to find a blemish on a lamb, they would approve it for sacrifice. But they perverted the Torah, turning their Levitical role into a business.