St. Robert Bellermine on grace's intrinsic efficacity

[Geremia]

Can efficacious grace be rejected?
Thomists believe that efficacious grace cannot be rejected, whereas Molinists think it can. The Church has not yet decided on the question.
From Fr. Garrigou-Lagrange's Grace, introduction:

these contradictory propositions: "Grace is intrinsically efficacious," and "Grace is not intrinsically efficacious," cannot be true at the same time or false at the same time; one is true, the other is false. The first is maintained by Thomism, the second by Molinism and likewise by the congruism of Suarez. Which, then, is true remains to be discovered.

Efficacious grace is (according to Fr. John Hardon, S.J.)

The actual grace to which free consent is given by the will so that the grace produces its divinely intended effect. In the controversy between the Dominicans [led by Báñez (1528-1604)] and the Jesuits [led by Molina (1525-1600)] there was no agreement on what precisely causes an actual grace to become efficacious. In the Báñezian theory, the efficacy of such grace depends on the character of the grace itself; in the Molinist theory, it depends on the fact that it is given under circumstances that God foresees to be congruous with the dispositions of the person receiving the grace. In every Catholic theory, however, it is agreed that efficacious grace does not necessitate the will or destroy human freedom. (Etym. Latin efficax, powerful, effective, efficient, gratia, favor freely given.)

Here's St. Augustine's view on efficacious grace, from his De praedestinatione sanctorum, chap. 8:

Grace which is not rejected by any hard-heartedness, since it is bestowed, in the first place, to remove hardness of heart.

and his De gratia Christi, chap. 24:

[Efficacious grace is the] internal, hidden, wonderful, and ineffable power by which God effects in the hearts of men not only true revelations but even upright wills.

cf. Grace ch. VIII "Excursus on Efficacious Grace"
So, "without me you can do nothing" (Jn. 15:5) is true even for disposing oneself to receive/accept grace in the first place (thus prevenient grace must be efficacious, else one could never begin to be sanctified).

St. Robert's opinion
St. Robert's views are found in his De gratia et libero arbitrio libri sex.
According to Pohle-Preuss's Grace, Actual and Habitual: A Dogmatic Treatise (Chapter III. Grace In Its Relation To Free-Will, Section 2. Theological Systems Devised To Harmonize The Dogmas Of Grace And Free-Will, Article 2. Molinism And Congruism),

Cardinal Bellarmine, who was a champion and protector of P. Molina, seems to have rejected Molinism⁷⁶⁵ in favor of Congruism.⁷⁶⁶

• Cfr. his treatise De Gratia et Libero Arbitrio, I, 12 [...]: "Prima opinio eorum est, qui gratiam efficacem constituunt in assensu et cooperatione humana, ita ut ab eventu dicatur gratia efficax, quia videlicet sortitur effectum et ideo sortitur effectum, quia voluntas humana cooperatur. Itaque existimant hi autores, in potestate hominis esse ut gratiam faciat esse efficacem, quae alioquin ex se non esset nisi sufficiens."
  

  Their first opinion is that efficacious grace consists in human assent and cooperation, so that from its occurence it is called efficacious grace, because it works its effect and thus achieves the effect, because the human will cooperates. So these authors think that it is within human power that grace is made efficacious, which otherwise of itself is only sufficient.

  Bellarmine treats this opinion as the extreme counterpart of Thomism (which he also combats) and disposes of it thus: "Haec opinio aliena est omnino a sententia b. Augustini et, quantum ego existimo, a sententia etiam Scripturarum divinarum." (l.c.)
  

  This opinion is entirely foreign to the thought of St. Augustine and, as far as I think, even to the thought of Holy Scriptures.

  Among the Scriptural texts which he quotes in support of this view are John VI, 45, 1 Cor. IV, 7, Rom. IX, 11.
• The learned Cardinal describes the difference between congruism and extreme Molinism (which latter, it may be remarked, was not defended by Molina himself) as follows: "Neque enim intelligi potest, quo pacto gratia efficax consistat in illa interna suasione, quae per liberum arbitrium respui potest, et tamen infallibilem effectum habeat, nisi addamus, Deum iis quos efficaciter et infallibiliter trahere decrevit, eam suasionem adhibere quam videt congruere ingenio eorum et quam certo novit ab eis non contemnendam." (Op. cit., [...])
  

  Nor can it be understood that efficacious grace consists in that internal persuasion which by freewill can be rejected and yet have an infallible effect, unless we add that God efficaciously and infallibly decreed they draw it, which persuasion He sees congruent with their innate nature and which He certainly knows they will not despise.

  The objection that this explanation eventually resolves itself into the Molinistic theory which he had censured, Bellarmine meets as follows: "Respondeo sententiam nostram, quam S. Augustini esse demonstravimus, aliqua in re cum prima illa opinione convenire, sed in multis ab illa discrepare. Convenit enim in eo quod utraque sententia gratiam sufficentem et efficacem ponit in auxilio excitante potissimum, non in adiuvante. Sed discrepant inter se, quod prima opinio vult efficaciam gratiae pendere a voluntate humana, nostra vero pendere vult a voluntate Dei." (l.c., cap. 13 [p. 294].)
  

  I answer that our opinion, which we have demonstrated is St. Augustine's, really agrees with that first opinion, but in many ways disagrees with it. It agrees with both opinions by putting sufficient and efficacious grace in the most powerful eliciting divine help, not in the one helped. But they disagree with each other, the first opinion wanting efficacious grace to depend on the human will, but ours wanting it to depend on the will of God.

^{(Improvements of the English translations, which are not in Pohle-Preuss, are welcome. ☺)}

Congruism
Fr. Hardon, S.J., defines "congruism" as:

The theory of man's co-operation with grace, first developed by Francisco Suárez (1548-1617) and St. Robert Bellarmine (1542-1621) and later adopted by the Jesuit order. According to congruism, the difference between efficacious and sufficient grace lies not only in the consent of the free will (Molinism), but also in the congruity or suitableness of a particular grace to the peculiar conditions of the one who receives the grace. When the grace suits the interior dispositions and external circumstances of a person, it becomes effective by the free consent of the will; otherwise it remains ineffective because it lacks free acceptance. As in Molinism, God foresees the congruity of the grace and its infallible success. Unlike Molinism, congruism places the emphasis not on man's freedom but on the supremacy of the divine will in determining salvation. (Etym. Latin congruitas, congruity, fitness, suitability, becomingness.)