Baptism is the entrance ramp to the Christian life. The Catechism calls it the “gateway” to the Christian life.
CCC 1213a Holy Baptism is the basis of the whole Christian life, the gateway to life in the Spirit (vitae spiritualis ianua) . . . .
The dichotomy of “grace” and supernatural faith, hope, and charity that is sometimes presented is a false dichotomy.
We receive supernatural faith, hope, and charity when we are Baptized (CCC 1813), even as infants (St. Thomas tells us [when discussing Confirmation but the same principle applies] we are not to think age of the body as being equivalent to age of the soul).
Supernatural faith, hope, and charity ARE graces! That is WHY they are called “supernatural”.
If a newly Baptized person virtually immediately dies, yes of course he/she will go to Heaven (and even an infant in this situation of immanent death should also be given Confirmation see CCC 1307 and the Eucharist although if they are not given these they will still go to Heaven).
So in that sense, yes a Baptized person will be saved. But there is MORE to the justification equation for most of us.
Once we are justified, we MUST be justified further still. That’s why our justification is a process—a lifelong process.
We MUST be “further justified”. This “further” justification of course depends on our state in life. It is not a legalistic checklist. An adult will have different expectations than a baby. This is part of the reason WHY we are “judged” and not “list-checked”.
Our justification is a moment followed by a lifelong process. And sins of omission not just committing mortal sin, but omitting the faith, hope, or charity we had received at Baptism can have disastrous consequences.
We must cooperate with grace. If we steadfastly refuse to cooperate with grace, we can accept the grace of God we received in vain. This grace will not avail us because of our rejection of it.
2nd CORINTHIANS 6:1 1 Working together with him, then, we entreat you not to accept the grace of God in vain.
Please also see Justification: Process or One-Time Deal?
Having been justified we are called to advance from virtue to virtue presenting them as instruments of justice unto sanctification through the observance of the commandments of God and of the Church. This is likely WHY sanctification and justification are so inter-related, that St. Paul can matter of factly remind us we are saved “through sanctification” in a state of grace (“by the Spirit”).
2nd THESSALONIANS 2:13 13 But we are bound to give thanks to God always for you, brethren beloved by the Lord, because God chose you from the beginning to be saved, through sanctification by the Spirit and belief in the truth.
Faith cooperating with good works, give us an increase in that justice received through the grace of Christ and we are further justified.
COUNCIL OF TRENT CHAPTER X
THE INCREASE OF THE JUSTIFICATION RECEIVED
Having, therefore, been thus justified and made the friends and domestics of God, advancing from virtue to virtue, they are renewed, as the Apostle says, day by day, that is, mortifying the members of their flesh, and presenting them as instruments of justice unto sanctification, they, through the observance of the commandments of God and of the Church, faith cooperating with good works, increase in that justice received through the grace of Christ and are further justified, as it is written:
[INDENT]He that is just, let him be justified still; and, Be not afraid to be justified even to death; and again, Do you see that by works a man is justified, and not by faith only?[/INDENT]
Someone might object and say: “Well someone who is just, let him be justified still more . . . . BUT . . . . it isn’t really necessary. It is an optional item as long as they don’t COMMIT a mortal sin.
But the CCC tells us we “MUST” increase in the Christian life.
CCC 162a,c Faith is an entirely free gift that God makes to man. . . . we must beg the Lord to increase our faith;45 it must be "working through charity," abounding in hope, and rooted in the faith of the Church.46
The Council of Trent tells us the same thing.
COUNCIL OF TRENT (Chapter XI) But no one, however much justified, should consider himself exempt from the observance of the commandments;
Sins of omission can have severe consequences, not just sins of commission.
MATTHEW 25:31-32a-33, 41-46 31 “When the Son of man comes in his glory, and all the angels with him, then he will sit on his glorious throne. 32 Before him will be gathered all the nations, . . . 33 and he will place the sheep at his right hand, but the goats at the left. . . . . 41 Then he will say to those at his left hand, ‘Depart from me, you cursed, into the eternal fire prepared for the devil and his angels; 42 for I was hungry and you gave me no food, I was thirsty and you gave me no drink, 43 I was a stranger and you did not welcome me, naked and you did not clothe me, sick and in prison and you did not visit me.’ 44 Then they also will answer, ‘Lord, when did we see thee hungry or thirsty or a stranger or naked or sick or in prison, and did not minister to thee?’ 45 Then he will answer them, ‘Truly, I say to you, as you did it not to one of the least of these, you did it not to me.’ 46 And they will go away into eternal punishment, but the righteous into eternal life.”