meaning, purport, drift
恉 centers on the underlying idea or intention behind something: its meaning, purport, or general drift.
恉 combines the heart radical 忄 with 旨, which likely contributes both sound and the idea of purpose or intention. The exact historical development is uncertain.
The heart 忄 beside 旨 (purpose) suggests the heart's intention: the meaning or drift behind one's words.
For シ, imagine the heart 忄 whispering 'she' knows the true meaning: she -> シ, and her heart grasps the purport.