Pertinacity, that is, obstinate adhesion to a particular tenet is required to make heresy formal .For as long as one remains willing to submit to the Church's decision he remains a Catholic Christian at heart and his wrong beliefs are only transient errors and fleeting opinions.Privation of faith is therefore the greatest evil, and deliberate rejection of faith is the greatest sin. But infidelity does this more than any other sin, for the infidel (unbeliever) is without the true knowledge of God : his false knowledge does not bring him help, for what he opines is not God : manifestly, then, the sin of unbelief ( infidelitas ) is the greatest sin in the whole range of perversity." And he adds: "Although the Gentiles err in more things than the Jews, and although the Jews are farther removed from true faith than heretics, yet the unbelief of the Jews is a more grievous sin than that of the Gentiles, because they corrupt the Gospel itself after having adopted and professed the same. That unity exists in the Catholic Church, and is preserved by the function of her teaching body: these are two facts which anyone can verify for himself. Arius appeared on the scene when theologians were endeavouring to harmonize the apparently contradictory doctrines of the unity of God and the Divinity of Christ.In the constitution of the Church there is no room for private judgment sorting essentials from non-essentials: any such selection disturbs the unity, and challenges the Divine authority, of the Church ; it strikes at the very source of faith. Instead of unravelling the knot, he simply cut it by bluntly asserting that Christ was not God like the Father, but a creature made in time. Intolerance and cruelty The term heresy connotes, etymologically, both a choice and the thing chosen, the meaning being, however, narrowed to the selection of religious or political doctrines, adhesion to parties in Church or State. Paul is described to the Roman governor Felix as the leader of the heresy ( aireseos ) of the Nazarenes ( Acts 24:5 ); the Jews in Rome say to the same Apostle : "Concerning this sect [ airesoeos ], we know that it is everywhere contradicted" ( Acts ). Justin (Dial., xviii, 108) uses airesis in the same sense. Peter (II, ii, 1) applies the term to Christian sects : "There shall be among you lying teachers who shall bring in sects of perdition [ aireseis apoleias ]".
Pertinacious adhesion to a doctrine contradictory to a point of faith clearly defined by the Church is heresy pure and simple, heresy in the first degree. completely ignoring the philosophy of the Schools and thus depriving themselves of the means of clearing away the confusion of their ideas and of meeting sophisms. If now we turn to the Modernist leaders for an account of their defections, we find none attributing it to pride or arrogance, but they are almost unanimous in allowing that curiosity--the desire to know how the old faith stands in relation to the new science --has been the motive power behind them. It is, therefore, advisable to leave individuals to themselves and to study the spread of heresy, or the origin of heretical societies. The heretical tenets may be ignorance of the true creed, erroneous judgment, imperfect apprehension and comprehension of dogmas : in none of these does the will play an appreciable part, wherefore one of the necessary conditions of sinfulness--free choice--is wanting and such heresy is merely objective , or material . The believer accepts the whole deposit as proposed by the Church ; the heretic accepts only such parts of it as commend themselves to his own approval.A man born and nurtured in heretical surroundings may live and die without ever having a doubt as to the truth of his creed.On the other hand a born Catholic may allow himself to drift into whirls of anti-Catholic thought from which no doctrinal authority can rescue him, and where his mind becomes incrusted with convictions, or considerations sufficiently powerful to overlay his Catholic conscience. Thomas, in the strict sense, are they who of their own will and intention separate themselves from the unity of the Church.