The society should set the ground for individuals to reach happiness in this world and the hereafter. Such a society needs precise and defined laws. Certainly, given its limitations, humanity cannot arrive at laws that can be applied at all times and in all places unless there is a connection to a supernatural source.
On the other hand, establishing order in society without the presence of people who defend observing laws and personal and social rights is not possible. That is why Islam introduces both laws and conditions for those who enforce the laws.
One of the manifestations of order is fulfilling promises because by observing order and though proper planning, the ground is set for fulfillment of promises.
The Holy Quran says in Verse 8 of Surah Muminoon: “(Prosperous are those) who preserve their trusts and pledges.”
The Holy Prophet (PBUH) said one who is not true to his promises is not a believer.
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It has also been emphasized in Hadiths that one should not look at how much people pray or fast to judge the level of their faith, but rather how faithful they are to their promises.
In the last moments of his life, the Holy Prophet (PBUH) told Imam Ali (AS) to return what has been entrusted to him, whether its owner is a righteous person or an evil-doer and no matter how insignificant it is.
The Holy Prophet (PBUH) was even careful about small details when came to being true to premises. Once a man told the Prophet (PBUH) to wait for him by a cliff. After some time, the sun began to bother him. His companions asked him why he did not move to the shade, and he said the place he had promise to wait was right there not in the shade.