One who truly observes fasting, with its spirit ingrained within, pondering over the Quran, it is in relation to them that Satan will be tied down. Satan can not be effective against them, he will not be able to exert his influence on them.
In the Hadith, many things are mentioned about Ramadan. So people also take it literally, because of which they do not understand its deeper meanings. For instance, it is mentioned in the Hadith that the devils are chained during the month of Ramadan. So people understand that they are physically tied up, that they are tied up and placed in confinement. But it does not mean that. This means that they are bound in relation to those who keep fast observing its spirit.
One who truly observes fasting, with its spirit ingrained within, pondering over the Quran, it is in relation to them that Satan will be tied down. Satan can not be effective against them, he will not be able to exert his influence on them. That's what it means. So, fasting prepares you in such a way that Satan cannot exert his influence over you. That's the meaning of this Hadith. While taking in its literal meaning, people think that Satan has been tied up somewhere or thrown onto an island. This is by no means the real meaning.