الْوَقْتُ يَمْضِي. فَابْدَؤُوا الْعَمَلَ.
Time passes. Therefore, begin the work.
The first clause asserts a fact; the second commands action. Separating them gives the news its own place, while fa marks an inferential connection. This is not the same as mechanically treating any link as coordination by wāw.
Even with separate sentences a discourse-level explanatory or inferential connection may remain. Rigorous analysis distinguishes syntactic conjunction from rhetorical resumption and causal sequencing.