How did 'decree' evolve from 'to separate'?

What's an intuitive derivation or rationale to help remember the definition? I purpose to burrow below definitions, which I already understand so ask NOT about. I heed the Etymological Fallacy.

decree = {noun} 1. An official order that has the force of law:

= {verb} [with object] Order (something) by decree

Etymonline: early 14c., from Old French decre, variant of decret (12c., Modern French décret), from Latin decretum, neuter of decretus, past participle of decernere "to decree, decide, pronounce a decision," from de- (see de-) + cernere "to separate" (see crisis).

My especial concern: How does "to separate" effect/imply/induce the definitions, given that "to separate" (the original) and order (modern) fail to relate to each other?

Footnote: Unhelpfully and oddly, OED's entries for the verb and the noun are both too terse.

As your research demonstrates, decree is related to crisis:

crisis:

early 15c., from Latinized form of Greek krisis "turning point in a disease" (used as such by Hippocrates and Galen), literally "judgment, result of a trial, selection,"

from krinein "to separate, decide, judge,"

from PIE root * krei- "to sieve, discriminate, distinguish"

(cognates: Greek krinesthai "to explain;" Old English hriddel "sieve;" Latin cribrum "sieve," crimen "judgment, crime," cernere (past participle cretus) "to sift, separate;" Old Irish criathar, Old Welsh cruitr "sieve;" Middle Irish crich "border, boundary").

Transferred non-medical sense is 1620s in English. A German term for "mid-life crisis" is Torschlusspanik, literally "shut-door-panic," fear of being on the wrong side of a closing gate.

Intuitively, when conflicting arguments were presented to a judge, he did what the PIE root and all of the cognates imply: he sifted through all of the evidence, discriminated between conflicting opinions, distinguished truth from fiction, decided the case, then explained his decision, which become the new boundary between the contestants. Our explicit discernment of that process may be clouded, but linguistically, the decree is the outcome of the crisis.

de- (concerning, down to the bottom, completely) + cernere (sifting, separation) yields:

concerning the judgement or complete judgement