The climax of a divine encounter often occurs not in what is seen, but in what is left behind when the vision ends. For a husband and wife witnessing a miraculous event, the sudden and permanent departure of their mysterious guest brings absolute clarity.
The primary approach among commentators is that the guest's ascent into the altar fire and his subsequent disappearance marked a complete turning point in Manoah's understanding. Up until that very moment, Manoah harbored doubts about the stranger's true nature. He assumed the visitor was simply a human being capable of performing wonders, and he even expected the man to step down from the altar and return to them [מלבי״ם]. Had the visitor interacted with the fire in any other way, it might not have provided conclusive proof. However, rising directly within the flame and vanishing completely proved beyond any doubt that this was not a flesh-and-blood human, but an angel returning to his heavenly place [מלבי״ם, ביאור שטיינזלץ]. Furthermore, Manoah's full realization was not triggered solely by the dramatic ascent in the fire. It was the fact that the angel departed entirely and never returned that cemented his understanding of what had just occurred [רד״ק].
The narrative focuses exclusively on Manoah's sudden realization, notably leaving out his wife. This highlights a gap in their awareness. His wife had already sensed much earlier that they were dealing with a higher being, having noted from the start that his appearance was like that of an angel. Manoah, in contrast, was a simpler man who failed to grasp the reality of the situation until the miraculous disappearance [אברבנאל].
Yet, even after recognizing the visitor as an angel, Manoah found no peace. He was overcome with terror, mistaking the angel for a direct revelation of God Himself. Driven by the ancient belief that any person who sees a distinct spiritual being is doomed to die, he feared their lives were at an end. In the face of this panic, his wife steps in to calm him with sound logic. She reasons that God's acceptance of their sacrifice, the wondrous events they witnessed, and the promise of a son being born all serve as clear evidence that He has no intention of putting them to death [אברבנאל].