Halakhah sobre Jonás 3:10

It is a positive commandment, ordained by the Prophets, to fast on those days on which tragic events occurred to our forefathers. The purpose of the fast is to stir our hearts to reflect on the ways of repentance, and to serve as a reminder of our own evil deeds,and the deeds of our forefathers, which were as reprehensible as ours, and caused all these troubles for them as well as for us. By remembering these events we will improve our ways, as it has been said, "They will then confess their sins and the sins of their fathers" (Leviticus 26:4). Therefore, it is everyone's duty to take it to heart on those days to examine his past actions and to repent; for fasting is not the main thing, as it was said about the people of Nineveh, "And God saw their deeds" (Jonah 3:10), and our Rabbis, of blessed memory, have said, "It does not say, 'He saw their sackcloth and their fast,' but 'God saw their deeds, that they had turned away from their evil ways.'" Fasting is only a preparation for repentance. Therefore those who while fasting, spend the time taking walks, and doing trivial things, take hold of the least important aspect of the fast, while ignoring the essence [of the fast.]