wide, large, enlarge
恢 centers on spaciousness and expansion: something wide, large, or made larger. The idea applies to physical space and to abstract scope.
恢 combines 忄 (heart/mind) with 灰, which likely contributes the sound. The compound suggests a broad or expansive mind, fitting the meaning of wide or large.
The heart radical 忄 beside 灰 (ashes) suggests a heart as wide as a field of ashes stretching far in every direction: wide, large, and expanding.
For カイ, imagine a wide, open sky (空, カイ) above a vast field of ashes: 空 -> カイ, and the heart expands to match that spaciousness.
heaven's vengeance is slow but sure; heaven's net is wide and coarse, yet nothing slips through
heaven's net has large meshes, but nothing escapes
propagation; spreading out; extending