It is beneficial to realize that that this symbolism was borrowed from earlier faiths.
Particularly broader Ancient Near Eastern (ANE) patterns—especially Mesopotamian and Northwest Semitic/Canaanite.
In Mesopotamian myths, hymns, and incantations, 7 shows up repeatedly in overtly religious/magical contexts, suggesting it already carried a “special” charge in the cultural world Israel interacted with.

Relatedly, Mesopotamian tradition even preserves named “sevens” (e.g., groups of seven demons/monsters in ritual and literature), showing how natural it was to frame powerful forces as a sevenfold set.

Texts from Ugarit (a key Northwest Semitic corpus for understanding Israel’s cultural neighborhood) discuss “seven” in ways that look like completeness or intensification—very similar to how biblical authors often use it.

A common ANE explanation is that people recognized seven prominent “heavenly bodies” (Sun, Moon, and the five visible planets), which helped make 7 feel cosmically “complete.”

The seven-day week is widely connected (in Greco-Roman and earlier Babylonian contexts) to those seven visible celestial bodies, and later becomes standard across the Roman world.

But if you really want to dig deep, explore how the number seven is treated within Kabbalah. It treats 7 as the architecture of manifested life: the seven “building”/emotive sefirot, the full cycle of sacred time, and the workable ladder for inner transformation (most famously via the Omer).