For anyone to be saved, he must have faith, hope and charity. These must be supernatural, i.e. they must be infused with sanctifying grace by God. These theological virtues can only exist in members of the Catholic Church.
This promise is made to each and every rational human creature. Not only are God's commandments reasonable and possible to fulfill, since God demands nothing beyond what nature can bear, but He continually offers His assistance to us, hence we NEVER have an excuse before God for committing ANY sin. It is in fact heresy to say otherwise:
Pope Innocent X, Cum Occasione, 1652, ex cathedra: "Some of God's precepts are impossible to the just, who wish and strive to keep them, according to the present powers which they have; the grace, by which they are made possible, is also wanting. - Declared and condemned as rash, impious, blasphemous, condemned by anathema, and heretical."
Every temptation or suggestion from the devil (which is not sinful of itself until it is granted consent of the will) is counter balanced by actual graces from God. These graces are not sanctifying grace, but rather the grace given to all men, Catholic and non-Catholic alike, whereby they are strengthened against temptation and sin, and which, if accepted and followed faithfully, would lead them into the Catholic Faith, and ultimately to Heaven.
Hebrews 11:6: " But without faith it is impossible to please God. For he that cometh to God, must believe that he is, and is a rewarder to them that seek him."
Pope Paul III, Council of Trent, Session 6, Decree on Justification, Chapter 1, ex cathedra: "(A)ll men had lost their innocence in the prevarication of Adam-having become unclean, and, as the apostle says, by nature children of wrath, as (this Synod) has set forth in the decree on original sin,-they were so far the servants of sin, and under the power of the devil and of death, that not the Gentiles only by the force of nature, but not even the Jews by the very letter itself of the law of Moses, were able to be liberated, or to arise, therefrom; although free will, attenuated as it was in its powers, and bent down, was by no means extinguished in them."
Romans 10:17: " Faith then cometh by hearing; and hearing by the word of Christ."
Pope Paul III, Council of Trent, Session 6, Decree on Justification, Chapter 6, ex cathedra: "(W)hile God touches the heart of man by the illumination of the Holy Ghost, neither is man himself utterly without doing anything while he receives that inspiration, forasmuch as he is also able to reject it; yet is he not able, by his own free will, without the grace of God, to move himself unto justice in His sight."
It is by accepting and acting on God's graces that men are drawn to the Faith of God. Having accepted His grace, they are more open to the Truth and, by God's help, have prepared themselves for the acceptance of divine light, whereby they may be profitably enlightened with the Gospel and the reception of sanctifying grace in Baptism, which renders them supernaturally good and pleasing to God. In Holy Baptism, the three supernatural virtues are immediately infused into the soul:
Pope Paul III, Council of Trent, Session 6, Decree on Justification, Chapter 7, ex cathedra: "(T)he instrumental cause is the sacrament of Baptism, which is the sacrament of Faith, without which (faith) no man was ever justified [...] For, although no one can be just, but he to whom the merits of the Passion of our Lord Jesus Christ are communicated, yet is this done in the said justification of the impious, when by the merit of that same most holy Passion, the charity of God is poured forth, by the Holy Spirit, in the hearts of those that are justified, and is inherent therein: whence, man, through Jesus Christ, in whom he is ingrafted, receives, in the said justification, together with the remission of sins, all these (gifts) infused at once, faith, hope, and charity."
Does God convert ONLY those who accept and comply with ALL his graces?
Such a position would be difficult indeed to support when considering the many sinners and infidels who have ultimately converted. St. Paul killed Christians before his conversion. St. Cyprian was a warlock in league with Satan before his conversion. St. Augustine was a lecher, and so on. And these (previously) mortal sinners became three of the holiest and greatest Early Christian Fathers ever! We must never lose sight that God may save whomever He will.
Romans 9:21: "Or hath not the potter power over the clay, of the same lump, to make one vessel unto honour, and another unto dishonour?"
St. Matthew 9:11-13: "And the Pharisees seeing it, said to his disciples: Why doth your master eat with publicans and sinners? But Jesus hearing it, said: They that are in health need not a physician, but they that are ill. Go then and learn what this meaneth, I will have mercy and not sacrifice. For I am not come to call the just, but sinners"
But God certainly does not owe sinners another day on this earth. Obstinacy in sin is asking for damnation. It is important to note that every human creature who dies in sin, or dies outside the true Faith of Jesus Christ goes straight to hell:
Pope Eugene IV, Council of Florence, Session 6, 1439, ex cathedra: "But the souls of those who depart this life in actual mortal sin, or in original sin alone, go down straightaway to hell to be punished, but with unequal pains."
Nevertheless, as long as the soul is united to the body, it has not been finally judged and there is time for mercy. No matter how hardened the sinner, we can, we may, and we ought to pray for his or her conversion right up until the end, since God's grace to convert even hardened sinners is powerful indeed if only they would accept it, as is clear from the beginning of the nineteenth chapter in St. Luke's Gospel. It is truly their choice. After that time, however, if they have run on to a final impenitence and died in mortal sin, no man may pray for them, as they have made the eternal and irrevocable choice of everlasting death.
1st St. John 5:16: "He that knoweth his brother to sin a sin which is not to death, let him ask, and life shall be given to him, who sinneth not to death. There is a sin unto death: for that I say not that any man ask."