‘And Ananias hearing these words fell down and gave up the life within him: and great fear came on all who heard it.'
The recognition that he had been exposed was too much for Ananias. His heart gave way and he breathed his last. He fell down dead before them all. If he had a weak heart the situation is quite understandable. But that we are certainly intended to see here a judgment of God comes out in what later happened to Sapphira. The point was made that God had struck him down. And the result was that all God's people were filled with awe and recognised even more that God was not to be mocked (Galatians 6:7).
There are certain times in history where particular sins were seen as having such vital importance that the only solution was the death of the perpetrator. One example is the sons of Aaron who at the very time of the institution of the priesthood offered false fire to the Lord (Leviticus 10:1-2). Another was Achan who on first entry into the land had ‘kept back' (in LXX same verb as in Acts 5:1 above) some of the booty of Jericho that had been specifically dedicated to the Lord (Joshua 7). In both cases instant death was the penalty. Those were times at the beginning of something new when an important lesson of obedience and respect for God had to be taught. The same was true here. All would now know that the new Kingly Rule of God was not something to be taken lightly.
But before we retire thankfully behind the misguided confidence that therefore God's people today need not fear the same thing happening we should remember the words of Paul, ‘for this reason there are many sickly among you, and many sleep' (1 Corinthians 11:30). God may not act in such a devastating way now as He did then, but He still does punish those who are careless about their behaviour, especially when it affects the wellbeing of the people of God. Much might be explained if we knew the hearts of men.