to stroke
捫 centers on a gentle, caressing touch: stroking or smoothing something with the hand.
捫 combines 扌 (hand) with 門, which likely contributes the sound モン. The hand radical suggests an action done with the hand, such as stroking.
The hand radical 扌 beside a gate 門: imagine gently stroking the smooth wooden surface of a gate with your hand.
For モン, picture a monk gently stroking the temple gate: monk -> モン, and his hand moves softly over the wood.