And almost all things are by the law purged with blood; and without shedding of blood is no remission. (Heb 9:22)
Our forgiveness comes from God - through Jesus' sacrifice. There is a line from one of my favorite television series in which one of the characters says "it's always about the blood". Blood is what nourishes our bodies. It supplies oxygen to our vital organs and removes the carbon dioxide. The exchanges of these gases takes place in the lungs - the literal "breath of life".
Jesus came to us in human form. He experienced all that we experience - the temptations, the need for nourishment - anything "human". This man did nothing to warrant the execution he received. He did it for us. He willingly went to the cross to open the gate to heaven and to offer forgiveness to all of us. He allowed the "life force" to be completely drained from his body. His lungs ceased to move air and his heart stopped beating. The same hands that healed were pinned above the level of his heart with nails similar to railroad spikes. He hung there until the last drop of his blood had left his body. And in that moment - he paid our debt!
Open your eyes to the sacrifice of Calvary. Use that as your measure of forgiveness toward others. What is there on earth that cannot be forgiven??? Is there anything so vile and ugly that you cannot release from your heart? There shouldn't be. Sin is sin - whether it's pocketing a piece of candy from the local convenience store, or the multi-billion dollar bank heist. Sin is sin - whether its an intentional harmful word or murder. Sin is sin - whether its of omission or commission. It can be and is forgiven if we ask. But in the asking, the effort to refrain from committing it again must also be present. Remission of our sins means we are released from the debt, obligation and penalty that would normally be expected from the commission of such. We are no longer required to pay for them - Christ did that for us. We are, however, accountable for them. We will answer for them, but those who have been "washed in the blood of Calvary" will stand, with Jesus, forgiven.
Continue to forgive those who ask; forgive those who don't ask! Those who crucified Christ did not ask for (nor did they feel the need for) forgiveness, yet he gave it to them willingly while he hung there dying. Ask God to remove the stubbornness from your heart. Let go of the anger that continues to cause you pain. And if you aren't sure if you can forgive that unspeakable hurt - you need only to look to the cross for your answer...