Can non-Catholics pray to God?
Some encouraging words
Once the necessary existence of absolute truth has been solidly argued, no reasoned opposition can be brought forth, as to contradict the notion of absolute truth, denies the very laws of logic themselves. These laws are necessarily broken by worldviews which deny the existence of absolute truth. Any religious doctrines, then, which claim to be true, must necessarily reflect a perfect self consistency, so as not to be toppled from within upon honest scrutiny of their teachings.
A person worships a false god when he believes and practices contrary to the true God's commandments, for the commandments of heretics and schismatics are the commandments of men (who have invented a religion after their own desires and therefore a god also) or the doctrines of devils, who since the fall, have wanted to covet the worship that is due to the Creator.
It is purely axiomatic (that is, self evident) to say that "those who worship in a false religion worship a false god". The statement would seem to require no further proof, as it stands on its own. Just because a heretic thinks he worships the true God does not mean that he does, any more than a Muslim, a Hindu or a Scientologist does. The fact is that each of these religions, while bearing some mark of truth (which comes from God) nevertheless also bears falsehood (which is from Satan or the inventions of man). The true religion, of course, has no falsehoods in it, unlike heresies. It is because of the falsehoods of heretical sects that heretics who find themselves saying such things as "Well the God I worship allows such and such a thing," or "the God I follow teaches this or that," are really laying claim to a false god as their master.
Maybe your god does allow or teach what you say, but the true God does not! If your god allows you to do something that is contrary to the true religion, then how can you say you worship the true God? You can't!
Christ Himself is recorded as having said as much, in various ways:
St. Matthew 7:22: "Many will say to me in that day: Lord, Lord, have not we prophesied in thy name, and cast out devils in thy name, and done many miracles in thy name? And then will I profess unto them, I never knew you: depart from me, you that work iniquity."
Just because heretics or schismatics invoke the name "Jesus" does not mean that they are worshiping the one true Jesus Christ, who came to earth to establish the Catholic Church for the salvation of souls. In the end, such people, when they see God at the end will be told by Him "I never knew you". Why? Because they are NOT His children. If they are not God's children, whose then?
St. John 8:42-44: "Jesus therefore said to them: If God were your Father, you would indeed love me. For from God I proceeded, and came; for I came not of myself, but he sent me... Why do you not know my speech? Because you cannot hear my word. You are of your father the devil, and the desires of your father you will do. He was a murderer from the beginning, and he stood not in the truth; because truth is not in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father thereof."
Heretics and schismatics are not doing the will of the Father when they blaspheme the doctrines of the Holy Catholic Church, when the invent false doctrines and encourage all manner of sins. They are doing the will of their father AND THEIR gOD, the devil.
St. Matthew 18:17: " And if he will not hear them: tell the Church. And if he will not hear the Church, let him be to thee as the heathen and publican."
1 Corinthians 10:20: "But the things which the heathens sacrifice, they sacrifice to devils, and not to God. And I would not that you should be made partakers with devils."
Heathens do not worship the true God, and neither do those who do not hear the Church. It is critical to salvation to understand this, lest we offend the true God, by likening him to the gods of heretics, who permit their "faithful" to enter the temples of idolaters or heathens (or Jews or heretics or Muslims) to pray.
Scripture is clear on the point that those who are worshiping in heretical sects, believing the lies and doctrines men and devils, rather than the truth of God, are not the children of God, and are as the heathens, who have not God.
Among the Fathers of the Church, this truth was particularly well expressed by the Holy Bishop St. Cyprian.
St. Cyprian of Carthage, Treatise 1: "The spouse of Christ cannot be adulterous; she is uncorrupted and pure. She knows one home; she guards with chaste modesty the sanctity of one couch. She keeps us for God. She appoints the sons whom she has born for the kingdom. Whoever is separated from the Church and is joined to an adulteress, is separated from the promises of the Church; nor can he who forsakes the Church of Christ attain to the rewards of Christ. He is a stranger; he is profane; he is an enemy. He can no longer have God for his Father, who has not the Church for his mother."
Finally, the Magisterium of the Holy Catholic Church makes it clear enough. It is a dogma of the Faith that without the Faith, a person is not a child of God (meaning their father can only be you know who).
Pope Pius IX, Vatican Council, Session 3 Chapter 3, #8-9, ex cathedra: "Wherefore, by divine and Catholic faith all those things are to be believed which are contained in the word of God as found in Scripture and tradition, and which are proposed by the Church as matters to be believed as divinely revealed, whether by her solemn judgment or in her Ordinary and Universal Magisterium.
"Since, then, without faith it is impossible to please God and reach the fellowship of His sons and daughters, it follows that no one can ever achieve justification without it, neither can anyone attain eternal life unless he or she perseveres in it to the end."
Heretics have not this faith, are not pleasing to God, are not His sons or daughters, but children of the devil, whom they unwittingly worship in the form of a false 'jesus christ' when they perform their profane rites and ceremonies.
St. Thomas Aquinas, Summa Theologica, Secunda Secundae Partis, Q. 10, Art. 3: "Every sin consists formally in aversion from God, as stated above (I-II, 71, 6; I-II, 73, 3). Hence the more a sin severs man from God, the graver it is. Now man is more than ever separated from God by unbelief, because he has not even true knowledge of God: and by false knowledge of God, man does not approach Him, but is severed from Him. Nor is it possible for one who has a false opinion of God, to know Him in any way at all, because the object of his opinion is not God."
What Must You Do To Get to Heaven?