The one all-powerful all-knowing God, who is Love, Mercy, and Justice by His very Nature, has freely chosen to offer forgiveness to all sinners, and salvation to all humanity. The offer is universal: all human persons without exception are offered forgiveness for every sin and eternal salvation in Heaven with God forever. The universal forgiving and salvific will of God is the teaching of Sacred Scripture and of the Roman Catholic Magisterium.
Since God is all-powerful and He wills all persons to be saved, do all persons eventually obtain eternal life in Heaven? The teaching of Tradition, Scripture, and the Magisterium on this point is clear and unequivocal: many souls are lost forever to the eternal punishments of Hell. For although the OFFER is universal, the ACCEPTANCE of that offer is not universal. Those human persons who sin gravely, and especially those who refuse to repent from grave sin, thereby refuse to live a life of love. They have, in effect, refused their own salvation. God is Love and Mercy, but He is also Justice, by His very Nature.
Does this possibility of eternal punishment, despite the universal salvific will of God, imply that God is not all-powerful? Not at all. For God is not merely powerful, He is infinite perfect Love. His power is His love, and His love is His power. And there is no love without free will. The basis for the forgiveness and salvation offered to all is LOVE: the love of God above all else and the love of your neighbor as yourself. But it would contradict the Nature of God as Love, if He were to compel, by mere power, all persons to be saved. And so, His all-powerful grace both makes our wills truly free, and permits us to freely decide: for or against forgiveness, and for or against true selfless love. If we reject forgiveness and love, we have rejected God and our own salvation.
Who, then, can be saved? In my book of Roman Catholic salvation theology, I argue that all persons can possibly be saved, including Catholics, Protestants, Jews, Muslims, and persons of any religion as well as agnostics and atheists, unbaptized infants and prenatals, persons of any age or condition of life, and even those who have fallen into a life of many grave sins. Non-Christians can be saved without converting to Christianity. Non-believers can be saved without converting to belief in God. The offer of forgiveness and salvation is universal, and is filled with the mercy and love of God. But the acceptance of that offer requires something of you. What is required?
You must enter the state of grace by some form of Baptism:
1. formal Sacrament of Baptism with water, or,
2. a baptism of desire, which might be implicit for some persons, or,
3. a baptism of blood, which I believe includes prenatals and children who die at a young age.
Then you must remain in the state of grace, or at least return to that state by repentance if you fall into actual mortal sin. Finally, you must die in the state of grace.
The state of grace is the state of loving God and neighbor. Whoever truly loves his neighbor, truly loves God (at least implicitly). Whoever truly loves God and neighbor is in a state of grace. The love of God and neighbor is the sole path to Heaven and eternal life.