In the Name of Allah, Most Gracious, Most Merciful.

All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.

Thank you for your good question. May you have a happy and blessed Ramadan, ameen.

The main objective of fasting is developing taqwa (consciousness of Allah). Allah Almighty says, {O believers! Fasting is prescribed for you—as it was for those before you—so perhaps you will become mindful of Allah˺.} (Al-Baqarah 2:183)

Therefore, a Muslim has to develop the moral of taqwa throughout the month of Ramadan.

As for the fast of those who commit sins, it is valid, though it is imperfect.

A person may not attain the reward of fasting because of committing sins. The Prophet (peace and blessings be upon him) said: “Whoever does not give up false speech and acting upon it, Allah has no need of his/her giving up his/her food and drink.” (Al-Bukhari)

Also, Abu Hurairah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “There may be people who fast and get nothing from their fast except hunger and thirst, and there may be those who pray qiyam (night prayer) and get nothing from their qiyam but a sleepless night.” (Ahmad)

May Allah accept your and our good deeds, ameen.

Allah Almighty knows best.