Books
If you wish me to weep, you yourself must feel grief.
— Horace · Ars Poetica

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker makes shared feeling a condition of moving another person. Wanting someone else to weep is not enough; the person trying to move them must first feel grief. The sentence links emotional expression with an inward experience rather than a desired outward response.
Context reviewed