look at
瞻 centers on directing one's gaze toward something: looking at or observing with attention.
瞻 combines 目 (eye) with 詹, which likely contributes the sound. The structure suggests using the eyes to look at something.
The left side is an eye 目, and the right side 詹 looks like a person peering over a cliff. Imagine an eye looking intently from a high vantage point.
For セン, picture a sentry using their eyes to look out from a high post: sentry -> セン, and the sentry's gaze matches 瞻.