According to Holy Mother Church, conversion is the work of the Holy Spirit.

am astound­ed that I have to set out to prove this, but there we are; the Church’s biggest mis­sion field is the Church. Let’s start with the Cat­e­chism of the Catholic Church (a very good place to start). There, in §1989, we read: “The first work of the grace of the Holy Spir­it is con­ver­sion, effect­ing jus­ti­fi­ca­tion in accor­dance with Jesus’ procla­ma­tion at the begin­ning of the Gospel: ‘Repent, for the king­dom of heav­en is at hand.’ Moved by grace, man turns toward God and away from sin, thus accept­ing for­give­ness and right­eous­ness from on high.”

Con­ver­sion (whether ini­tial con­ver­sion or con­tin­u­ing con­ver­sion) is all gift and all grace, and indeed the Coun­cil of Trent teach­es that apart from the grace of the Holy Spir­it, con­ver­sion is impos­si­ble:

It is fur­ther­more declared that in adults the begin­ning of that jus­ti­fi­ca­tion must pro­ceed from the pre­dis­pos­ing grace of God through Jesus Christ, that is, from His voca­tion, where­by, with­out any mer­its on their part, they are called; that they who by sin had been cut off from God, may be dis­posed through His quick­en­ing and help­ing grace to con­vert them­selves to their own jus­ti­fi­ca­tion by freely assent­ing to and coop­er­at­ing with that grace; so that, while God touch­es the heart of man through the illu­mi­na­tion of the Holy Ghost, man him­self nei­ther does absolute­ly noth­ing while receiv­ing that inspi­ra­tion, since he can also reject it, nor yet is he able by his own free will and with­out the grace of God to move him­self to jus­tice in His sight.

Let’s unpack this. The Coun­cil is say­ing that, while it is true that a con­vert must say “yes” to God, it is only by the grace of God act­ing in him that he is able to say “yes” at all. Mary said “yes,” but she was able to say yes because of the pre­ve­nient grace of the Immac­u­late Con­cep­tion.

Christ affirms this in John 6:44: “No man can come to me, except the Father which hath sent me draw him.” It is impor­tant not to inter­pret John 6:44 in a Calvin­ist man­ner and say that the verse teach­es lim­it­ed atone­ment or irre­sistible grace. But it does teach pre­ve­nient grace: apart from being drawn, we would be pow­er­less to come.

Con­tin­u­ing conversion—or “per­se­ver­ance,” if you will—is also the grace of the Holy Spir­it, accord­ing to Trent:

He that shall per­se­vere to the end, he shall be saved, which can­not be obtained from any­one except from Him who is able to make him stand who stands, that he may stand per­se­ver­ing­ly, and to raise him who falls, let no one promise him­self here­in some­thing as cer­tain with an absolute cer­tain­ty, though all ought to place and repose the firmest hope in God’s help.

I owe my con­ver­sion to God. End stop.

I owe my per­se­ver­ance to God. End stop.

And though it is true I must say “yes,” with­out Him who is able to make me stand, I could not stand.

Grace is all; and all is grace.

And if I were to fall away, how might I be restored? The Coun­cil of Trent answers that ques­tion too:

Those who through sin have for­feit­ed and received grace of jus­ti­fi­ca­tion, can again be jus­ti­fied when, moved by God, they exert them­selves to obtain through the sacra­ment of penance the recov­ery, by the mer­its of Christ, of the grace lost.

And so Canon 3 of the Decree on Jus­ti­fi­ca­tion says:

If any­one says that with­out the pre­dis­pos­ing inspi­ra­tion of the Holy Ghost and with­out His help, man can believe, hope, love or be repen­tant as he ought, so that the grace of jus­ti­fi­ca­tion may be bestowed upon him, let him be anath­e­ma.

What enables con­ver­sions is “the pre­dis­pos­ing inspi­ra­tion of the Holy Ghost.” The Coun­cil of Trent says noth­ing about Caje­tan’s pre­dis­pos­ing refu­ta­tion of Luther, or New­man’s pre­dis­pos­ing apolo­gia pro vita sua.

Of course it is true that God can use Caje­tan, or use New­man, to help con­vert a soul. That is not in dis­pute. They are God’s fel­low work­ers; amen dico tibi. And sim­i­lar­ly, water is God’s fel­low work­er when God uses water to wash away sin.

But apart from the action of God, water is just water and a priest’s hands are dust and clay.

Apart from the action of God, the best apolo­getic argu­ment in the world for becom­ing Catholic is just paper.

It is the gift of God, lest any man should boast (Eph­esians 2:9). St. Thomas Aquinas con­sid­ered his works and said: “Straw.”

Apart from the breath of God, no breath in us and no life.