Catholics these days alas seem ignorant of grace: yet as St Thérèse said, Tout est grâce - All is grace.
It is absolutely vital not to imagine, as too many do, that we are entitled as of right to heaven!
We are not.
Of ourselves, we cannot deserve heaven.
But God, in His superabounding love, wills to lift us up to share His Life.
Grace is simply a gift, a Godlike gift: the word gratia means a gift given gratis, for free. It is a kingly and Godlike gift, literally.
Every good and every perfect gift comes from above, coming down from the Father of lights. (James i, 17a)
The Holy Spirit is Himself Uncreated Grace; acting in our souls, He grants them something above and beyond our natural powers: grace is a supernatural addition to the soul - we remain human, but gain something beyond the human.
By His Passion, our Saviour Christ has merited every gift and grace for us all.
Through the gift of faith, a grace given by God, we come to seek Him. His is always the initiative! But when we respond, He responds right marvellously, giving us entrance into His Communion through the Sacrament of Baptism.
Baptism is the salvific command of Christ: He merited its grace, He is the True Priest Who acts through whosoever baptises, He is the Holy One into Whom we are baptised.
By Holy Baptism, the life of the Trinity is infused into us: we are supernaturalized, made capax Dei - "capable of God"! This is to be graced, to have our soul permanently changed, inexpressibly, for the better. The graced soul is made fit for heaven: for grace is the seed of heavenly glory.
Baptism makes us Christians: we are forever marked by this transformation, we receive an indelible character: we are stamped with the seal (sphragis) of the Trinity, we are incorporated into Christ, made truly His, a Christian, brought into His Body, into His Bride, the Church. Even a renegade Christian burning in Hell is still forever marked with the baptismal character...
Grace is divided into many categories: for supernaturally meritorious acts, we receive actual graces that we then coöperate with and act upon; for as long as we are "in the state of grace", we possess habitual grace. If lamentably we fall into mortal sin, we lose the state of grace, but, by receiving actual graces that move us to repentance and Confession, we are brought back to being in habitual grace - while the baptismal character remains, though horribly disfigured by mortal sin.
According to the axiom of classical scholasticism, God the First Cause, and ourselves as secondary causes, are equally truly the cause of our actions. In the case of an action done under the inspiration of grace, God is of course the Cause of it, and it is thanks to Him that we have done good; but we are also the cause, because moved by His grace to freely act, and so we have done good - hence, both all is grace, and we in Christ do truly merit supernatural reward - a higher degree of heavenly glory.
Glory be to God for His inexpressible gift! (II Cor. ix, 15)