Grudge, spitefulness are the rejection of love. God is love and if you are holding a grudge against someone, then you deny true love, which is God.
Approximately, this is how St. Ignatius Brianchaninov writes and adds that God withdraws from a spiteful man and deprives him from His grace.
Dear people, here is why many of us consider ourselves as “good Christians, go to church every Sunday, but the promises of God about peace and joy aren’t always manifested in our lives. It’s because many of us don’t know how to truly forgive each other from the bottom of our hearts and not hold grudge against one another.
Do not be spiteful, forgive one another, don’t hold grudge, don’t think bad against your friends or neighbors, just leave everything to God. Doing this won’t hurt you. Instead, it will liberate you from these negative and sinful passions and will fill your heart with Divine presence.
This is a wonderful feeling.
Otherwise, “if you do not forgive others their sins, your Father will not forgive your sins.” Matthew 6:15