What did Gandhi hope to achieve through the civil desobedience calling on all Indians to observe "a day of prayer and fasting"

Through the civil disobedience Gandhi told the Indians to observe "a day of prayer and fasting" as they wanted to make them strong mentally for this movement.

Explanation:

The motive of calling a one day fasting is to make the Indians more strong against the British government. Prayer is the way of reminding God for strength and power to fight against the wrong activity.

The Civil Disobedience Movement was one of the mass movement launched by the Indian National Congress against British imperialism. By 1929, India began to doubt the intention of Britain whether it would execute its declaration of grant of colonial self-government or not. The Indian National Congress announced at the Lahore Session (1929 AD) that its goal was to achieve complete independence for India.