But there are two sins, not of individual deed, but of spiritual condition, which cannot be forgiven; that is, as it seems to me, which cannot be excused, passed by, made little of by the tenderness even of God, inasmuch as they will allow no forgiveness to come into the soul, they will permit no good influence to go on working alongside of them; they shut God out altogether. Therefore the man guilty of these can never receive into himself the holy renewing saving influences of God’s forgiveness. God is outside of him in every sense, save that which springs from his creating relation to him, by which, thanks be to God, he yet keeps a hold of him, although against the will of the man who will not be forgiven. The one of these sins is against man; the other against God.

The former is unforgiveness to our neighbor; the shutting of him out from our mercies, from our love—so from the universe, as far as we are a portion of it—the murdering therefore of our neighbor. It may be an infinitely less evil to murder a man than to refuse to forgive him. The former may be the act of a moment of passion: the latter is the heart’s choice. It is spiritual murder, the worst, to hate, to brood over the feeling that excludes, that kills the image, the idea of the hated.

—From Creation in Christ by George MacDonald

For those with ears to hear, listen and understand.