First, we are going to verify that there is something immaterial in man that cannot be identified as being made of any specific matter.
The water that flows through our organism isn’t the same today as tomorrow, because we eliminate the water we drank yesterday and we ingest water again; with the sugar we need, greases, proteins or phosphorus we do the same. Thus, after a time, the matter we have in our body is completely different from the one we had before (that is so, even considering that there are brain cells that live a long time, or even the whole life of man on earth, but, according to physicians and biologists, its material composition is not the same after a longer or shorter period (fixed by some people at seven years)).
That’s why, when we say that man is composed by matter, we cannot say by this or that specific matter, because there isn’t any specific matter that stays permanently in man. Nevertheless, although the matter of my body has changed, we can say that I am the same person as yesterday. Therefore, there must be some immaterial element inside me that is still the same and assures that I’m the same today as yesterday. In the changing matter of the human body, there must be something that subsists, that remains, making possible that the mentioned human being stays the same, assimilating, giving life to the matter, the food that he or she takes in. Antiquity called that remaining thing that cannot be reduced to matter “form” and the specific form of the human being was called “soul” (see Objections for a more accurate explanation).
Moreover, there are events which give us joy or pain, without affecting our body: It is not our body the one who feels, but another part of our being: the soul:
“How can atheistic psychiatrists explain the joy for the fulfilled good action or the remorse for the evil done? Where does such a big joy or such a big pain come from? May be from a part of our body? This offence that we receive directly or indirectly from another person, in a letter or by phone, that makes us suffer so much… has it perhaps hit some specific limb of our body? Has it not rather hit our soul? There are things which satisfy the senses, i.e., the body, but there are others that, without touching the body, give pleasure or pain to the soul i.e. to that spiritual element that we call soul which gives form and life to the body”.(“La medida está colmada”, O. Michelini, PG. 156)
Let’s choose now a new point of view: If the human being were only matter, it would be logical to think that his or her way of acting has to be submitted to physical and chemical laws, that his or her behaviour can't escape and go beyond the laws of Nature and of the instinct: but we meet people like Maximiliam Kolbe, who was in a POW camp and being a witness to the death penalty of a father who was his companion, offered himself to replace him in the cruel sentence: he gave his life for his captivity companion, and he encouraged his fellow prisoners who were going to be put to death like him to sing and praise God. If we have an instinct that urges us to preserve life, and there are men who overcome it for reasons of superhuman love, this is a piece of evidence which proves that man is able to act above his animal and material nature: i.e. inside man there is something which raises him over nature.
Every man can carry out more or less heroic actions enhancing his value.Thus, in man there is something higher than the mere material and animal nature. This thing is called soul.
The above was to establish that in man there exists an element that is not matter, although we have not yet said that this element called “soul” is immortal.
Man aspires to full happiness and he would prefer never to die. That’s every man’s wish. In this life, the wish for a perfect happiness is unreachable and, besides, we know that, sooner or later, everyone of us must die. If the soul died with the body, it would mean that God had instilled a wish and an aspiration in man’s nature we cannot fulfil.
But we see in nature how babies are born searching with its lips where to suck, and the mother’s nipple exists, the same way as when we are thirsty the water also exists and when we are hungry the food exists as well. Then, if we are hungry and thirsty for happiness and for immortality, it means that the perfect happiness and eternal life do exist. God, who is the only good being, would not have put in our hearts such a wish, if He didn’t want to see it fulfilled. So, since we see that the body dies, we must think that we have a source that lives for ever inside us (and that will animate our bodies again when the resurrection of the bodies arrives).We call such source, that does not die, the soul.
Besides, the soul being immaterial, it has no parts at all, and when it separates from the body it doesn’t have to be corrupted or broken up.
Furthermore, we realize what would happen if God would allow the destiny of oppressors and men who offer their life in a sacrifice of love, to be the same: that of rotting in the grave. He would be an unfair God. In order that God can reward the good ones who sometimes suffer on this earth, and punish the bad ones who sometimes appear as having a nice time in this life, it is necessary that man’s soul be immortal. Special mention must we made of the suffering of innocent people: it would be a big injustice that there were not another life after death.
If no other life existed, men wouldn’t have any incentive to be virtuous, and the wicked ones would be able, repeating the words that the Wisdom Book puts on their lips, to laugh at God’s justice oppressing the helpless:“For they said among themselves, thinking not aright, “Brief and troublous is our lifetime; Neither is there any remedy for man’s dying, nor is anyone known to have come back from the nether world. For haphazard were we born, and hereafter we shall be as though we had not been…Come, therefore, let us enjoy the good things that are real, and use the freshness of creation avidly…Let us oppress the needy just man; let us neither spare the widow nor revere the old man for his hair grown white with time…Let us beset the just one, because he is obnoxious to us…”
(The Book of Wisdom, 2, 1-12)
Such are the thoughts of evil men and they would be right if man wasn’t immortal in his better part: the soul. As the Book of Wisdom tells us:“These are their thoughts, but they err; for their wickedness blinds them. And they knew not the hidden counsels of God neither did they count in a recompense of holiness, nor discerned the innocent soul reward. For God made man to be imperishable…(Wisdom, 2, 21-23).
And describing the punishment of evil ones in the other life, this same book of the Bible tells us:
“Fearful shall they come, at the counting up of their misdeeds, and their transgressions shall convict then to their face” (Wisdom 4, 20)
“Then shall the just one with great assurance stand before his oppressors…(Wisdom 5, 1). “They (the evils) shall say among themselves rueful and groaning…”(Wisdom 5, 3) “Fools that we were! His life we meeded madness, and his death dishonoured,,,”, “We, then, have strayed from the way of truth, and the light of justice did not shine for us, and the sun did not rise for us”(Wisdom 5, 4-6)
But in case one doesn’t believe in immortality, the door to all kind of crimes gets open and life in society becomes like life in the jungle, where the wicked one oppresses the honest one without punishment. Hence, there must be another life where God gives His reward or His punishment to both of them, and that is also an incentive or leash in this life, so that society can be just. Therefore, the soul is immortal.
From the immaterial nature of the soul, from the wish of perfect happiness and immortality dwelling in every man’s heart, which according to every law existing in nature, must be fulfilled, and from the fact that a God that is good has put it in our heart and will satisfy it, from the injustice it would be that God left our life in earth without praise or punishment, from the confusion that would bring in our present life the contrary belief that we die and all is finished, it follows that man’s soul is immortal.