Interesting Posts from everyone, very insightful and knowledgeable. One sin leads to another, as Jesus said if your eye causes you to sin pluck it out, it's better to go Blind throughout life than offend God. Having said that when someone covets or has lust for something, it is already a sin, because it will most likely lead to more or worse sins. There are degrees of sins, obviously murdering your neighbor is more severe than lying to your boss about the real reason you were late for work. As Christians we must avoid the occasion for sin meaning putting our selves in a place or situation where we could easily be tempted by the Devil. For example walking into a strip club, hanging out with drug addicts etc. This is what Jesus was mentioning about committing a sin "In your heart" specifically what is your intention looking at a woman in a lustful way? Surely not a good one. Then letting oneself to be overwhelmed with lustful desires will eventually lead to committing more grave offenses towards Our Lord.
Patience and self control are great virtues on the eyes of God, The Apostles had to face great temptations while promoting and protecting Jesus' name and Holy Word, they even had to stare death in the face, but still didn't weary in their support of Our Lord Jesus. Pray to God and he will help us, as scripture says " I can do all things through Him who Strengthens me."
God Bless.