There are many believers who feel the need to fast and intercede for their family, friends and loved ones . It is important to know what will nullify our fasting and we learn of it in Isaiah 58:1-12.
Let us not just go through the outward motion of fasting and expect God to answer us.
Dispel the delusion that God would be satisfied with outward observances, while the spirit of the law, was violated and the heart unchanged. Do not mock God.
Matthew Henry’s Concise Commentary
58:3-12 A fast is a day to afflict the soul; if it does not express true sorrow for sin, and does not promote the putting away of sin, it is not a fast. These professors had shown sorrow on stated or occasioned fasts. But they indulged pride, covetousness, and malignant passions. To be liberal and merciful is more acceptable to God than mere fasting, which, without them, is vain and hypocritical. Many who seem humble in God’s house, are hard at home, and harass their families. But no man’s faith justifies, which does not work by love. Yet persons, families, neighbourhoods, churches, or nations, show repentance and sorrow for sin, by keeping a fast sincerely, and, from right motives, repenting, and doing good works. The heavy yoke of sin and oppression must be removed. As sin and sorrow dry the bones and weaken the strongest human constitution; so the duties of kindness and charity strengthen and refresh both body and mind. Those who do justly and love mercy, shall have the comfort, even in this world. Good works will bring the blessing of God, provided they are done from love to God and man, and wrought in the soul by the Holy Spirit.
So do not fast if there is no change of heart to receive God’s blessings.
Instead, turn from our wicked ways and He will hear us.