Presumption is here considered as a vice opposed to the theological virtue of hope. It may also be regarded as a product of pride. It may be defined as the condition of a soul which, because of a badly regulated reliance on God's mercy and power, hopes for salvation without doing anything to deserve it, or for pardon of his sins without repenting of them.In the above quote from the 1913 Catholic Encyclopedia, we are given the difference between presumption and hope. Some may think that this is merely an academic issue that is splitting hairs in a theological debate, but that would be a false presumption (pun intended). When we seek to place our hope in God, there is a right way to do that, and a wrong way. When we ignore our own circumstances and try to bank merely on God's willingness to forgive, we have greatly misunderstood what hope is.
Hope, which is so greatly needed today, is a reliance on the promises of God. This means that we must know what the promises are if we are going to rely on them. If we believe that God has promised to provide us with monetary wealth in this life, and we maintain "hope" in that (faulty) promise, then we do have hope; it is, however, a hope in something that is false, and that is not the virtue that we are called to have. The theological virtue of hope is always grounded in truth (not in our selfish desires).
The Lord is certainly able to provide us with monetary wealth (it is not as though He is incapable), but since He has not promised that (and sometimes promised the opposite!) we cannot ground our hope in a lie. This is what the Catholic Encyclopedia refers to as "a badly regulated reliance on God's mercy". No one should say that we should not rely on God's mercy, but there comes a time in which that reliance has become something other than godly hope if we have distorted the promises of God into a list of self-serving daydreams.
The monetary wealth falsehood (though not much of a concern in the Catholic Church) is a fairly easy point to make. Catholics pretty much know that this is not how God does things. A much more challenging issue comes up when we begin to seek to hope in a promise regarding our eternal salvation. That is the real issue that the Encyclopedia is concerned about. Hoping for salvation without doing anything to deserve it (works of faith and charity, etc.), or hoping for forgiveness without repentance are not truly the virtue of hope; that is what we call presumption.
As a protestant I experienced many different groups and denominations whose entire understanding of Christian salvation was based on a presumption. Scriptures were twisted to serve personal ends in ways that would make most logician's heads spin. In their desire to avoid anything that appears to look like the holiness the Catholic Church encourages, they sought out ways to justify a novel idea of salvation. For those who have been taught this understanding of salvation, I can understand they want to hold to it; for us as Catholics, we should not be copying that grave error.
I recall once having someone say to me that he did not really need to go to confession because he knew that God was merciful and would forgive his sins whether or not he told them to a priest. That is presumption, not hope. Notice how the Encyclopedia quote above refers to a "badly regulated" reliance. What would lead someone to have a badly regulated reliance? It stems largely from either a badly formed conscience, or a badly informed understanding of the faith (or both!). Therefore, let me ask the simple question: what are you doing to properly form your conscience and your understanding of the faith? What did you do today? What did you do last week? Are you doing anything towards those ends?
To sit back and presume that God's mercy will save someone who is impenitent even when 2000 years of Church teaching says otherwise is not even a Christian response. It is, in fact, just like the Encyclopedia says: a "product of pride". When we focus on ourselves and presume upon our well being, we pridefully ignore what the clear testimony is and then fall into a presumption about our eternal status. "I can keep sinning like I am and it will all work out in the end because God is merciful" is not found on any of the Saints' lips.
Should we trust in God's mercy? Yes! In the right context and with the right understanding of what mercy really is (as well as what hope really is). A blind, or foolish trust in something that looks like God's mercy is not what we are supposed to do though, and there are many who fall into this category today. Where is your trust? Where is your hope? Is it in something that contradicts the clear testimony of the Church? Are you relying on God to go against all that He has revealed in His Word? If so, then you have no hope; all you have is presumption.