It is not sinful to have a large bank account, where you are not worried about paying the next bill and have plenty of money left over.
However, being rich does come with it a greater responsibility, as God will require an account of how you used your money for the benefit of others.
Poor in spirit
St. Francis de Sales writes about this topic in his Introduction to the Devout Life. He explains that we need to recognize how our money and possessions are not truly our own:
My child, our possessions are not ours,—God has given them to us to cultivate, that we may make them fruitful and profitable in His Service, and so doing we shall please Him. And this we must do more earnestly than worldly men, for they look carefully after their property out of self-love, and we must work for the love of God.
One way to protect ourselves from getting too greedy with our money is to be constantly giving it away:
To this end always dispose of a part of your means by giving them heartily to the poor; you impoverish yourself by whatever you give away. It is true that God will restore it to you, not only in the next world, but in this, for nothing brings so much temporal prosperity as free almsgiving, but meanwhile, you are sensibly poorer for what you give. Truly that is a holy and rich poverty which results from almsgiving.
St. Francis de Sales also explains the importance of simply loving the poor, which will help us remain poor in spirit:
Love the poor and poverty,—this love will make you truly poor, since, as Holy Scripture says, we become like to that we love. Love makes lovers equal. “Who is weak and I am not weak?” says St. Paul? He might have said, Who is poor and I am not poor? for it was love which made him like to those he loved; and so, if you love the poor, you will indeed share their poverty, and be poor like them.
If we do not seek out the poor and desire only to amass a large amount of money for ourselves, God will be much harsher with us on the day of judgement.
When God gives us many gifts, he does so that we may be generous with them, not keeping them for ourselves, but giving them to others.
