Catholics may faithfully disagree with the Roman Pontiff to a fairly wide extent:
However, there are limits, beyond which the disagreeing Catholic is committing an objectively grave sin. The knowing obstinate refusal to believe an infallible teaching of the Magisterium is formal heresy, which carries the penalty of automatic excommunication. Anyone who is automatically excommunicated may not receive holy Communion.
Schism is another type of grave sin which carries the penalty of automatic excommunication.
Canon 751: “schism is the refusal of submission to the Supreme Pontiff or of communion with the members of the Church subject to him”.
Canon 1364, n. 1: “an apostate from the faith, a heretic, or a schismatic incurs a latae sententiae excommunication”
If you think that Pope Francis is wrong about a bunch of different things, you might still be a faithful Catholic. But perhaps you are the one who is wrong. And if you can’t admit that possibility, you may be guilty of the sin of pride.
If you take it a step further, by deciding that Pope Francis has gone so far astray from the Church that he has lost his authority to teach and guide the faithful, or that you will no longer accept him as Supreme Teacher and Supreme Shepherd, or anything similar (or anything worse), then you have fallen into the sin of schism. No matter the reason, if you refuse to submit your mind and heart to the authority of the Roman Pontiff over doctrine and discipline, you have sinned gravely. And that sin is called formal schism.
If so, then you are not permitted to receive holy Communion. If you continue to receive holy Communion, while unrepentant from the objective mortal sin of formal schism, you receive unworthily. In such a case, your reception of Communion is an additional grave sin. You sin by receiving our Lord in Communion, unless you first repent.
It is ironic that, in a dispute over who may receive Communion, some Catholics have become unworthy to receive Communion themselves. For they commit formal schism against the one true Church, and schismatics may not receive.
What if a Catholic who rejects Pope Francis feels, in his own conscience, that he is worthy to receive? What if he prays and decides that God does not mind? Isn’t that exactly the position on Communion for the divorced and remarried which the papal critics adamantly reject? They say that the divorced and remarried have committed an objective grave sin, and so they may not receive. And yet some of these papal critics have committed a different objective grave sin, without repentance, that of schism.
Anyone guilty of formal heresy or formal schism is not permitted to receive holy Communion.
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