Summary

Portrait of Thomas Aquinas Thomas Aquinas Summa Theologiae — Question 80 - OF THE USE OR RECEIVING OF THIS SACRAMENT IN GENERAL…

But in a measure the sin of fornication makes one more unfit for receiving this sacrament, because thereby especially the spirit becomes enslaved by the flesh, which is a hindrance to the fervor of love required for this sacrament.
However, the hindrance to charity itself weighs more than the hindrance to its fervor. Hence the sin of unbelief, which fundamentally severs a man from the unity of the Church, simply speaking, makes him to be utterly unfit for receiving this sacrament
Source: Wikisource

Portrait of Thomas Aquinas Thomas Aquinas Summa Theologiae — Question 80 - OF THE USE OR RECEIVING OF THIS SACRAMENT IN GENERAL…

The fact of a man being unconscious of his sin can come about in two ways. First of all through his own fault, either because through ignorance of the law (which ignorance does not excuse him) , he thinks something not to be sinful which is a sin, as for example if one guilty of fornication were to deem simple fornication not to be a mortal sin; or because he neglects to examine his conscience, which is opposed to what the Apostle says (1 Cor. 11:28) : "Let a man prove himself, and so let him eat of that bread, and drink of the chalice."
Source: Wikisource

Portrait of Thomas Aquinas Thomas Aquinas Summa Theologiae — Question 80 - OF THE USE OR RECEIVING OF THIS SACRAMENT IN GENERAL…

I answer that, A distinction must be made among sinners: some are secret; others are notorious, either from evidence of the fact, as public usurers, or public robbers, or from being denounced as evil men by some ecclesiastical or civil tribunal. Therefore Holy Communion ought not to be given to open sinners when they ask for it.
Source: Wikisource

Get perspective with Kwize: daily news enlightened by great literature