While living in a monastery with brethren, regard only yourself as a sinner and all the brethren without exception as angels.
I've found from experience that this applies equally to everyone, not just monastics. In married life, if I have this attitude towards my wife, any bitterness or resentment that may have built up disappears. If I spend my time focusing on my own sins and failings, regarding my own wife "as an angel," I find peace in myself and peace in my family. Why should I worry, after all, about the sins of others when I have a host of my own personal sins to deal with? Didn't Christ tell us to remove the board from our own eyes before removing the splinter from our brother's? St. Ignatius goes on to tell us:
Through humility in your dealings with your neighbor, and through love of your neighbor, hardness and callousness is expelled from your heart. It is rolled away like a heavy rock from the entrance to a tomb, and the heart revives for spiritual relations with God for which it has been hitherto dead.
I have always found it sad whenever I've seen spouses - whether in real life or as portrayed in the media - living in little more than a passive-aggressive relationship with years of bitterness, resentment, fault-finding, pettiness, etc., etc., etc. I've seen women roll their eyes every time someone mentions their husband's name. I've seen men's gaze turn cold at the sight of their wife. I know of couples who divorced and families that were torn apart because the spouses were overly concerned with each other's faults and sins rather than focusing on their own.
Obviously I would not condone that one spouse become the doormat of the other, allowing the other to trample them down and oppress them. Obviously couples need to work together for the betterment of each other on the physical/material, emotional, psychological, and spiritual levels. But an unhealthy focus on the other's faults does not lead to such betterment, especially when such a focus leads us to ignore our own faults.
St. Ignatius' advice could be equally applied to the workplace, parish life, our network of close friends, our extended family, etc., etc., etc. St. Seraphim of Sarov had a saying that has since become quite famous in Byzantine spirituality: "Acquire the spirit of peace, and thousands around you will be saved." That, I believe, pretty much sums up the teaching the St. Ignatius is presenting to us in his book.
I remember a story from St. Therese of Lisieux's diary Story of a Soul. It seems that while in the convent there was one nun who was particularly nasty towards Therese, whether because of her youth, her innocence, or what we do not know. But Therese, instead of responding in kind, went out of her way to be kind to this nun and to treat her with the utmost love and respect. Over time Therese's love wore down the walls of anger in this old nun's heart and drew her not only to a love and affection for Therese, but also into a deeper love for Christ. Here we see a wonderful illustration of St. Ignatius' teaching in action.
In closing I would simply like to point out how we can apply this to our praying the Jesus Prayer. Common English translations of the Jesus Prayer would have us say, "Lord Jesus Christ, Son of God, have mercy on me a sinner," as though we were simply one sinner among many. But it is possible for the Prayer to be translated from the Greek as, "Lord Jesus Christ, Son of God, have mercy on me the sinner." This would perhaps be more in keeping with the vision of St. Ignatius, and would give us a solid grounding in prayer to treat all our neighbors as though they are angels and we are the only sinner among them. May heaven consume us!