‘Therefore rejoice, Oh heavens, and you who dwell in them. Woe for the earth and for the sea, for the Devil has gone down to you having great wrath, knowing that he has but a short time.'
The heavens and the Heaven dwellers can rejoice at the Devil's defeat. These Heaven dwellers include those who have no permanent interest in earth but who look for a city which has foundations, whose builder and maker is God (Hebrews 11:10), prospective Heaven dwellers. These Heaven-dwellers are in contrast to the Earth-dwellers - ‘those who dwell on the earth' - i.e. non-Christians, a constant refrain in Revelation. It is the earth who will suffer for his downfall, for the Devil will seek to take out his wrath on them. That is why Peter can describe him as going around ‘like a roaring lion seeking whom he may devour' (1 Peter 5:8).
‘Knowing that he has but a short time'. Like everyone else Satan was expecting the end of the age soon. The time when Christ would come was known to no one. Not understanding the longsuffering of God he could not believe it would be long delayed. Thus he measured his behaviour by that belief. And indeed his time was and is limited. In God's ‘short time' all will be over.