When one learns that "modernism" is a heresy, one might spontaneously think that the Church is against everything that is contemporary. In fact this is not the case. Modernism posits that the only credible authority for any religious belief is personal feelings and experiences; that there are no philosophically sound reasons and no objectively verifiable evidence that proves one faith is truer than another, including the Catholic faith. Modernism denies the foundations of authentic Catholicism, and has led to the rampant spread of three errors that undermine a real understanding of the faith.
The first disastrous result of modernism is that the supernatural aspects of our faith are either marginalized or neglected. Some aspects of this neglect are evident. If you attend Mass for any length of time in the average Canadian parish, there will hardly ever be any homilies on heaven, hell, the salvation of souls, the intercession of saints, grace, holiness, the end times, or other topics connected with the divine and the economy of salvation; you will hear of social justice, personal relationships, or inner healing. Although these are important elements of our religion, they are not the core beliefs. The central message of Christian Revelation is that Jesus Christ is God incarnate who died for the sins to the world to reconcile humanity to God. Even if modernist priests or other religious elites refer to these notions from time to time, their overall discourse lacks a sense of the transcendent and of the divine because they bring up these topics so infrequently. They give the impression that the doctrines connected to salvation are not the most essential truths of the faith, the ones believers should keep uppermost in their mind. Note that few modernists deny these beliefs. They simply give them enough lip service to appear sufficiently orthodox, but in fact they focus on the temporal with little reference to them. In the modernist perspective, religion is largely a matter of what is immediately lived and felt. Damnation and salvation are minor issues, if they are relevant at all. Mortal sin, if it is said to exist, matters much less than feeling unforgiven, or living in a state of psychological rebellion against God.
The marginalization of the supernatural also occurs in a more insidious manner. If you examine the statements of modernists taken individually, there will often be no obvious error in them. The modernist way is to bring up a Catholic dogma, but never address the substance of its contents. It makes the dogma represent something other than what it literally is. It is perfectly acceptable to view dogma as symbolic of something else. The crux of the problem is that while modernism discusses the symbolism of the dogma, it never teaches the literal meaning of the dogma; its contents are systematically ignored, while the symbols of dogma become the primary focus of belief.
For instance, in the modernist view, the Resurrection is less about the rising of the dead than about the victory over suffering; and the Sacrament of Reconciliation is less about the conveying of sanctifying grace to a penitent than about being a symbol of God's love and mercy. Of course the Resurrection is a symbol of victory over suffering, and of course the Sacrament of Reconciliation is a symbol of God's love and mercy. These are perfectly acceptable ways of looking at it. But that is not their primary significance. The problem is that this "theological symbolism", as Pope Pius X termed it, coupled with the consistent neglect to emphasize the literal meaning of dogma, leads to the impression that modernist symbolism has replaced dogma as the focus of the faith. Catholicism is portrayed as no longer being a transcendent religion concerned about salvation and Last Things. Catholicism becomes a religion about the here-and-now, feeling good, getting along and making life more bearable here on earth. Since the modernist priest does not necessarily say anything objectionable, the sense of orthodoxy of the unsuspecting Catholic is satisfied, thereby pre-empting accusations of error or heresy. In this manner, modernism is permitted to take hold in the hearts of the faithful. Once Catholic dogma is emptied of its substance, its also emptied of its logic, leaving a philosophical vacuum where modernist thought can flourish.
Once he divests Catholic teaching of its supernatural essence, a modernist naturally concludes that truth is essentially relative. It "evolves". Divine Providence and Revelation are not actually what they are said to be by the Catholic Faith; they are only symbols. The Truth is what people believe is true, because the only truth one can know is what one experiences, thinks or feels. Magisterial pronunciations are only "working documents", subject to revision as the personal feelings and experiences of the faithful demand. If a personal experience is perceived to invalidate Catholic doctrine, then personal experience trumps magisterial authority, because magisterial authority is external and only the inner person can ratify belief.
This leads to a third negative consequence of modernism. If the supernatural is marginalized, and truth is relative, and the only ultimate authority is one's inner self, then logically one must conclude there is a right to "faithful dissent". This is the case of people who disagree with the Church teaching on contraception. Most Catholics are ignorant of their faith, and are imbued with modernist notions. They do not understand how the Church's teachings can be true. Instead of believing Church teaching on its divinely mandated authority, they refer to their own subjective experience. Contraception seems to work for them, makes their lives convenient, and has no apparent affect on their souls. It is natural for them to believe this, since they do not believe that lovemaking is essentially something supernatural. They figure truth is relative anyway, and they are their own authority in matters of their behaviour. Their beliefs are reinforced by erring religious elites who essentially subscribe to the modernist view of the primacy of the conscience without reference to Catholic teaching. They will leave teachings to an individual's conscience without insisting that it be formed by Catholic Revelation. Why would they, if they think that it's not an objective truth in the first place?
Modernism can only be countered by Catholics who know their faith well, and who can identify modernist ideas and statements. Modernism is so widespread among priests, academic, and laypeople in charge of teaching the faith that credentials and experience alone are not always a guarantee of orthodoxy. The only way to tell whether a source is trustworthy is to compare what he says (or fails to say) against the teachings of the Church, particularly the Catechism. Modernists count on their ideas sounding sufficiently orthodox so that no one will suspect them of being unfaithful to the Magisterium. This is how their ideas are spread. They use this apparent orthodoxy to dismiss those who understand the underlying premises of their thought, premises which modernists themselves fail to acknowledge. We must insist on injecting the supernatural into Catholic teaching and preaching, and on remaining true to the meaning of doctrine.