The heated debates in the Synod of Bishops regarding the possibility of divorced and remarried Catholics receiving Holy Communion have opened up a series of other important discussions, especially concerning the relationship between mercy and justice and between charity and truth. How can these seemingly opposing principles be lived out by the Church in the real world?

While one side argues for the importance of doctrine regarding the permanence of the sacrament of matrimony, the other side advocates just as passionately for the preeminence of mercy in the Christian life, and the need to meet people where they are, with all their wounds and weaknesses.

In this dramatic context, it may be opportune to take a small step backwards in order to examine the underlying understanding Catholics have about what it means to receive the Eucharist in the first place, and when — if ever — one should abstain from doing so.

One of the key lines that has been repeated multiple times in Rome in the past few weeks is Pope Francis’ celebrated maxim that the Eucharist “is not a prize for the perfect but a powerful medicine and nourishment for the weak.”

This beautiful expression is both a rebuke to the proud and an encouragement for those who acknowledge their unworthiness to receive Holy Communion, which Catholics believe to be the real body and blood of Jesus Christ. Who, after all, on careful self-examination, finds himself to be truly “worthy” to receive the Lord in Holy Communion? The Eucharist is no gold star on the forehead of “good” Christians, but an undeserved gift to strengthen pilgrims who stumble along through life with their gaze fixed on heaven.

As the great doctor of the Church St. Ambrose wrote: “If, whenever Christ’s blood is shed, it is shed for the forgiveness of sins, I who sin often, should receive it often: I need a frequent remedy.”

St. Thomas Aquinas drew an intriguing comparison between the life of the body and the life of the soul, suggesting that each of the sacraments corresponds to an event or element of our natural existence. Just as baptism corresponds to birth, and confirmation to the passage to adulthood, he called the Eucharist “spiritual food and spiritual medicine,” corresponding spiritually to the nourishment and healing brought about by food in our bodily lives.

But here we run upon a further argument that must be addressed.

Catholics believe that not all sins carry the same weight or have the same effect on our souls, and traditionally make a clear distinction between “mortal sins,” which separate a Christian from the life of grace, and “venial sins,” which do not. In the text of his First Letter, St. John already speaks of a sin that leads to death (pros thanaton), as opposed to a sin that does not lead to death (me pros thanaton) — referring here to a spiritual death.

Moreover, in speaking of the Eucharist, St. Paul writes that whoever “eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord” and then adds that a person “should examine himself, and so eat the bread and drink the cup.” (1 Cor 11:27-28)

Clearly, then, for St. Paul, though no one is truly worthy to receive the Eucharist, there is a sort of unworthiness that needs to be addressed before approaching the table of the Lord. The Catholic Church has traditionally understood this sort of unworthiness to be a state of having committed a mortal sin.

The way that this is expressed in the Catholic Catechism is that anyone “who is aware of having committed a mortal sin must not receive Holy Communion … without having first received sacramental absolution.” (No. 1457)

Aquinas, carrying on his analogy between the spiritual life of the soul and the natural life of the body, explains this by saying that the Eucharist is food, but food only helps the living. The one who commits a mortal sin “is not alive spiritually, and so he ought not to eat the spiritual nourishment, since nourishment is confined to the living.”

While Holy Communion, like bodily food, strengthens the weak and helps heal the infirm (which Aquinas equates with venial sin), it does not raise the dead. This, he said, is what the sacrament of penance or reconciliation is for.

The Church sees the state of grace — the life of the soul — to be a minimum condition or a low bar, so to speak, to be able to fruitfully receive the Eucharist. But that should be the only reason. As Aquinas says further: “Mortal sin alone necessarily prevents anyone from partaking of this sacrament.”

In the celebrated phrase quoted above from Pope Francis’ letter Evangelii Gaudium, he continues by saying that everyone can share in some way in the life of the Church and the doors of the sacraments should not “be closed for simply any reason.” By adding the clause “for simply any reason,” Francis seems to suggest that there can be serious reasons for abstaining from receiving the Eucharist, but that one shouldn’t do so lightly.

For the upcoming Jubilee Year of Mercy, Pope Francis has paid special attention to the sacrament of reconciliation, noting over and over again that there is no sin that God cannot forgive. He has hammered home the message of God’s infinite mercy, urging all the Catholic priests in the Church to dedicate plenty of time each week to hearing confessions.

Earlier this year, Pope Francis told a group of priests that their first task was to help penitents experience God’s mercy. “Confession should not be a ‘torture,’” he said, “but everyone should leave the confessional with joy in his heart, his face beaming with hope,” even if sometimes “wet with tears of conversion and the joy that comes from it.”

As the pope has taught that no one earns Communion, so no one earns God’s freely given gift of mercy, either. But it’s there for the taking.