We can often be down on ourselves, especially the scrupulosity that can arise in us as believers. It is very easy to see ourselves as unworthy and then to extend that to others and their unworthiness. We also have an amazing ability to blame something or someone else for our failings.
Mark was a hermit, but as we know that does not mean distancing one's self from others. He was also a prolific writer, taking on a multitude of issues and doctrines. One such group that he took on was the Messalian heresy, one that may not be familiar to most of us. They believed that each person has a personal demon so powerful that even baptism cannot conquer it or remove it from our lives.
Certainly the Devil is not destroyed by Baptism nor is his power to lie and temp removed by Christ's death on the Cross (even the demons that Christ exorcised roamed about looking for a new host). That is not the way God works. The power of Baptism and the Cross lie in their ability to save us, to help us overcome the power of Satan. To free us from the power of sin, to take responsibility for our actions and be penitent and atone for the wrongs we do. It frees us to do the good, to be like God in His holiness.
Our salvation is a partnership between us and God, an agreement, a Covenant. We do not accomplish it on our own nor do we accomplish it without doing anything. There is a fine balance like the balance between humility and scrupulosity.
Mark reminds us that we must rely on God not on our own selves for mercy.
Do not claim to have acquired virtue unless you have suffered affliction, for without affliction virtue has not been tested.
-- On the Spiritual Law
Wishing to show that to fulfill every commandment is a duty, whereas sonship is a gift given to men through His own Blood, the Lord said: ‘When you have done all that is commanded you, say: "We are useless servants: we have only done what was our duty" (Luke 17.10). Thus the kingdom of heaven is not a reward for works, but a gift of grace prepared by the Master for his faithful servants.
-- To Those Who Think to Be Justified by Deeds