For if a preest be foul, on whom we truste,
No wonder is a lewed man to ruste;
And shame it is, if a prest take keep,
A shiten shepherde and a clene sheep.
– Geoffrey Chaucer
The Canterbury Tales, General Prologue. If a priest goes bad and becomes corrupt, then it is no surprise that the common person should rust, metaphorically speaking, and go to the bad. This passage about the Parson says it is a shame to see a soiled shephard and a clean flock.