One of the glories of the Catholic faith is its pure simplicity and its simple purity. And this is all that is required of us: a purity of heart, a singlemindedness of desiring Heaven.
Purity and simplicity share in common with each other the notion of clarity. Everything we need to know in the Catholic Church is very clear — purity, simplicity, bound together with clarity.
For example, the teaching on the Blessed Sacrament, the Real Presence — that Jesus Christ is really, truly and substantially present, Body, Blood, Soul and Divinity, under the appearance of bread and wine. Can't get much more straightforward than that. And don't make the mistake that just because something is cloaked in mystery that it isn't clear. The how or why or even what of something doesn't detract from its simplicity or purity.
The Host, which looks and tastes like bread, is Jesus Christ, pure and simple. So, too, is the Church's teaching that if a person is to be saved, he must not die in a state of mortal sin. He must die in a state of grace — meaning sanctifying grace, meaning having the Holy Trinity living, abiding in him. This, too, is a pure and simple teaching. Depart from this life without the indwelling of the Holy Trinity, and a person remains in that state forever, without end.
This is Hell because at death, the soul experiences an illumination of reality: that what really mattered was its condition before God. God does not "know" a soul without Himself present in that soul at the moment of death. He Himself attests to this in the gospels when He says quite clearly of those knocking on the door to get in: "Go away. I tell you, I do not know you."
God is life. A person that dies in mortal sin has a soul without life, the requisite spiritual life of the Holy Trinity. Dying in that state, the soul is forever sealed in that state. In a somewhat crude analogy, a team with fewer points than the opponent when the final guns sound loses the game. That loss is forever sealed, locked, unchangeable. The competition is unrepeatable; the loss stands forever as a sign of failure to achieve the goal of victory.
So why should so many people have such a struggle with the concept of eternal damnation? It's a very simple and pure concept, extremely straightforward. Reject God and His loving commandments in this life, and a person is forever sealed in that condition of rejection of God. Likewise, live a life of desire to cling to God in this life by following the commandments of love — and that choice is ratified for eternity.
The Son of God commanded that a person be baptized and eat His Body and drink His Blood. He then underscored that unless you do this, you have no life within you. So how could a soul which departs this life without the life of God suddenly attain the life of God after death? The time for choosing is this side of death, not the next. It's pure and simple.
A soul must depart this life in a state of grace, with the life of God inside, and the surest means to do that is as a baptized, Holy Communion-receiving, with no conscious knowledge of mortal sin person. Everything else for a rational, non-invincibly ignorant person is a gamble in the extreme, and more than likely a losing proposition.
The line from the psalm "Deep is calling on deep" is most instructive here. When we stand before Almighty God, what He will search us for is the image of Himself. To the degree that we image Him, then deep calls on deep, and deep responds and goes to deep — like things to like things.
But when God calls out to the soul before Him at the Judgment, and that soul is spiritually dead, in a state of deadly sin, then there is nothing deep within that soul to respond. Here we have two things that are not alike, and as such, the soul with death flees from the God of Life and prefers the torments of eternal loss to the even greater torments of being in a state of constant death surrounded by life.
This is why the Church, members and leaders, must never retreat from the truth, from its purity, simplicity and clarity. Those who do betray the Lord of Life and demonstrate a frightening lack of love for souls.
The faith is simple because it flows from and back to God, Who is simple in Himself. The faith is pure because God is one. The faith is blinding in its clarity because God is. Our call is to conform to God in the way He commands us, pure and simple.