Genesis 1:3 (KJV)
And God said, Let there be light: and there was light.
What's the meaning of the word "let"?
Is the meaning closer to:
cause/effect, i.e. physics-related; or
allow/permit (cf), i.e. freewill-related; or
We are lucky! Very often, the exact nuance of an imperfect form is uncertain. This is because the original Semitic short and long imperfect (two distinct forms) merged relatively early in Hebrew due to loss of unstressed word-final vowels. Hence, the semantic difference between these two forms is not indicated by morphology any more. However, in some cases, with geminate and III-ה roots, the distinction is retained. And here we have a III-ה root, היה "to be".
The form in Gen 1:3, יהי, is a short imperfect (the long form is יהיה). Short imperfects have the most specific semantics: deontic modality and the completed past (hence their use in the wayyiqtol narrative tense). (Long imperfects can be used for a variety of semantic fields: present-future, epistemic modality, imperfective aspect, ...). Since completed past does not make sense in context (*God said, "there was light", and there was light), the form must indicate deontic modality here: "there must/should be light".
It then aligns most with what you call will-related. It is also a kind of performative speech, where by uttering something it is achieved (e.g., "You are hereby dismissed"). Performative speech is of course frequent with powerful entities such as kings and God.
For more information on the short/long imperfect distinction, see Holger Gzella, 2013: 'Northwest Semitic Languages and Hebrew' in G. Khan (ed), Encyclopedia of Hebrew Language and Linguistics.