inn, hut, house, mansion
舍 centers on a building where people stay or live: an inn, a hut, a house, or a mansion. The scale varies, but the core idea is a dwelling or lodging place.
舍 is a pictograph of a roofed structure with an opening, representing a simple dwelling or shelter. The modern form retains the roof-like top and the base 口 suggesting an entrance or foundation.
The top looks like a roof, and the bottom 口 is the entrance. Picture a small inn or hut with a wide-open door welcoming travelers.
For セキ, imagine a weary traveler checking into an inn and finding a cozy seat by the fire: seat -> セキ, and the inn provides rest.