The familiar use of «لو» (law) is to suppose a condition contrary to what occurred, commonly in relation to a past event. Its full meaning nonetheless depends on how the sentence is constructed.
«لو جاء زيد لأكرمته»
Had Zayd come, I would have honored him.
Zayd’s arrival is presented as a contrary-to-fact supposition, not a report that he arrived. The consequence is tied to that supposition; one should not infer every detail of the actual situation from the particle alone.
In broad contrast, «إن» leaves the condition open, «إذا» treats an event as envisaged, and «لو» readily depicts an unrealized alternative.