What does it really mean when we say that? Why is that, when we have done a wrong or committed a sin, most of us are haunted by "something"? That "thing" is, of course, our conscience. The word conscience means "with-knowing". This knowing is what keeps us accountable to God, to society and to our own deepest self. Theologians tell us that there are two types of conscience - anterior and subsequent. Anterior conscience is what we use when we are searching and deliberating about what we should do in a particular situation. Subsequent conscience is when we look back and examine an action or decision already made.
The challenge for us as Christians is to make sure that always seek to better form our conscience so it is capable of leading us to good moral choices and of examining choices already made. We do this in prayer by asking God to reveal to us our own "dark side" so that we can continue to improve. We also do this in study by reading and understanding Scripture, digging into the Catechism and other trustworthy resources, and by taking time every day to reflect on our thoughts and actions. In the end we rely on God's grace given through the Sacrament of Reconciliation to propel us to a saintly lifestyle.
I am attending a 4-hr talk this Friday on "conscience". I'll write more on this when I process the speaker's message.

In Luke's version of the beatitudes, he states them a little differently than Matthew. Instead of saying "blessed are the poor in spirit" he just says "blessed are the poor". The conclusion to his version has the "woe to's", where he admonishes those with wealth by saying things like "Woe to you who are rich, for you have received your consolation" (Lk 6:24). Sayings like this to the people of his time were shocking because the prevailing belief was that the rich were blessed by God and the poor were cursed. If you read all of Luke's Gospel, indeed if you all of what Jesus said in his lifetime, you learn that the poor do have a special place in his heart.