The problem with his sermon was that he forgot one important definition. That without grace from God, we are not pleasing to God. And, this gift is given to those gratuitously by God. We cannot earn grace nor do our good works merit grace without God taking the initiative and removing sin from our lives through baptism and confession.
The priest was attempting to help people see that the circumstances of our lives were the raw materials of graced moments. But, he fell into Semi-Pelgianism, implying that we can save ourselves by responding to circumstances. Not so.
However, one cannot merely talk about grace without understanding that grace is not circumstance or illness or even material benefits. Graces cannot be equated with material or physical gifts. We use this term in colloquial talk, but grace is much more complicated to understand that this simplistic view.
Here is only one section from Garrigou-Lagrange's work Grace in which he reviews and unpacks St. Thomas Aquinas' treatises on grace. I use blue type for commentary.
The remission of guilt is inconceivable without an infusion of grace.” This reply contains two elements: 1. the remission of guilt is in fact produced by an infusion of grace, and 2. it cannot be effected otherwise, even by the absolute power of God.
There is no justification from sin without grace from God.
The first of these is of faith; the second is opposed to Scotus, the Scotists, and Saurez.
Definition of faith by the Council of Trent (Sess. VI, can. 10 and 11; Denz., nos. 820, 821):
“If anyone should say that men are just without the justice of Christ whereby He merited our justification or by that justice itself formally, let him be anathema.” “If anyone should say that men are justified either by the sole imputation of the justice of Christ or by the remission of sins alone, excluding grace and charity which is poured forth into their hearts by the Holy Ghost and abides in them, or even that the grace whereby we are justified is only a favor from God, let him be anathema.
Grace is not merely gift or favor. It is the sharing of the love of God within us. We are not empty vessels after we are baptised. Christ earned this on the Cross. And the Holy Trinity abides in us.
This article of the Church’s faith is clearly based on Sacred Scripture: “Of his fullness we all have received, and grace for grace” (John 1:16); “The charity of God is poured forth in our hearts, by the Holy Ghost, who is given to us” (Rom. 5:5); “To every one of us is given grace, according to the measure of the giving of Christ” (Eph. 4:7).
From the day of our baptism and hopefully, unless we commit mortal sin, all of our lives, we live in this sanctifying grace. This grace is a "gift" but it is won by Christ and granted in baptism, not in some circumstantial manner, but in a specific manner, through the sacraments of the Church.
Theological proof. St. Thomas shows the very impossibility of the remission of sin without the infusion of grace, thus admirably founding his argument on God’s love for us.
The remission of sin is effected according as God is pacified in our regard, loving us with special benevolence. But God cannot love the sinner with a special love except by infusing grace whereby the sinner is intrinsically transformed and made pleasing to God. Therefore the remission of sin cannot be effected without an infusion of grace.
Grace takes away sin through God's love. God does the transformation in us at baptism, as until then, we are not pleasing to Him. Original sin is taken away and God loves us with "a special love". All the action is on the part of God, not dependent on our reactions to circumstances in our lives. If we are already in grace, these circumstances can help us gain merit.
The major is self-evident, for God cannot remit the offense of the sinner unless He makes peace with him, and God makes peace with us inasmuch as He loves us with a special love. Thus nothing else can be designated wherein our peace with God consists; in other words, God makes peace with us in the matter of our offense on account of His special benevolence toward us.
Peace comes with justification in grace. God alone produces all that is good in us. We cannot do this.
The minor is based on St. Thomas’ principle enunciated in Ia IIae, q. 110, a. I, and Ia, q. 20, a. 2, to the effect that “the love of God does not presuppose goodness in us but produces it”; “the love of God infuses and creates goodness in things,” since He is the author of all good. Nor are we here concerned with the general love whereby God loves and preserves the very nature of the sinner while he is in the state of sin, but rather with the special love whereby He remits or pardons the offense.
Yes, God loves us while we are still in the state of sin but with a special love He pardons us. We are not pleasing to God until we are free from sin, and then He gives us grace to continue growing in love in Him.
This special love cannot but produce some effect in us, that is, it cannot help but make man pleasing; otherwise God’s created love for us would be no more effective than the love of our friends, who cannot change the interior state of our souls.
This grace is always efficacious. God begins the good work in us and sees it to completion. Only God can change us, make us perfect. We cannot do this by sheer effort or by merely responding to the circumstances of life.
Now habitual grace excludes mortal sin absolutely, which is precisely the privation of the life of grace, or the death of the soul. (Cf. ad I.)
Liivng in habitual grace means that one is living in sanctifying grace. If one sins mortally, one now lives outside of grace and one cannot please God.