year end sacrifice, dried meat
腊 centers on meat prepared for ritual or preservation: a year-end sacrifice involving meat, and dried meat as a preserved food.
腊 combines the meat radical ⺼ with 昔, which likely contributes the sound and possibly the idea of something old or past, fitting dried meat or an ancient sacrifice.
The meat radical ⺼ beside 昔 (old times) suggests meat from the past: either dried for preservation or used in an ancient year-end sacrifice.
For セキ, imagine a sacred year-end sacrifice where the dried meat is placed on a stone seat: seat -> セキ, tying the ritual meat to the reading.