I’ve noticed that “growing in holiness” is usually presented by popular Catholic media as something like “We just gotta pray more and try harder, then the Lord will make us holier.” As if becoming holy will take a lot of work, but God makes it possible. Similarly, we often speak of grace as sort of a spiritual vitamin or, as one book I recently saw put it, “The Eucharist gives me the energy to pursue holiness.”
That is, we speak of grace as something added to our efforts that makes them holy or fruitful. We presume that we are the primary actor in our own sanctification.
This is precisely what the pope describes as the new Pelagianism. That is, we “speak warmly of God’s grace” but really we believe that “all things are possible by the human will, as if it were something pure, perfect, all-powerful, to which grace is then added” (Gaudete et Exsultate 49).
Grace isn’t a spiritual energy boost, it’s the very life of God within us, transforming us into God. As the Catechism says, “Grace is a participation in the life of God. It introduces us into the intimacy of Trinitarian life….The grace of Christ is the gratuitous gift that God makes to us of his own life, infused by the Holy Spirit into our soul to heal it of sin and to sanctify it” (CCC 1997, 1999).
With that in mind, growing in holiness is grace making us like Jesus, divinizing us. The Holy Spirit is the first and primary actor, we simply cooperate with each step He is calling us to in our daily life.