In the Name of Allah, The Most Gracious, Most Merciful
Allah the Almighty says:
﴾ Observing As-Saum (the fasting) is prescribed for you as it was prescribed for those before you, that you may become Al-Muttaqun﴿
Taqwa (piousness) is the wisdom behind Siyaam according to the above Ayah. Taqwa in Arabic means protection, which saves man from harmful things. In this sense, Taqwa is your shield against Allah's Torment, Wrath, and Resentment, the loss of the Hereafter and misery. How can I protect myself from Allah's Resentment? I do that by obeying Him. How can I protect myself from Allah's Wrath? I do that by acting upon His Order and remain steadfast on His Path.