I’m a Thomist Catholic too, so I understand your thinking and your post. No. 137.
I believe CCC 600 but we Thomists have to be very careful with it because can be easily misunderstand if we don’t interpret it according to the teachings of Thomism and the Scripture.
Most of the paragraphs of the Catechism built on Thomism and the Scripture, but the CCC 600 among the few paragraphs which built on Molinism.
In order to understand the difference between Thomism and Molinism first we have to understand the differences the way God’s graces works in Thomism and in Molinism.
THE WAY GOD’S GRACES WORKING IN THOMISM and we may say in the Scripture and in the paragraphs of the CCC built on Thomism.
The Mystery of Predestination by John Salza.
Man always freely rejects sufficient grace, if the grace is efficacious, then man freely cooperates with it.
This is way St. Paul in Philippians 2:13 says that God works in man both to will (operating grace) and to accomplish (cooperating grace).
God wills the grace to be either sufficient or efficacious from the very beginning of the operation.
A sufficient grace has an operating effect only (empowering the will to act),
whereas an efficacious grace has both an operating and cooperating effect (applying the will to act).
When God wills a person to perform a salutary act (e.g., prayer, good works), He grants him the means (an efficacious grace) that infallibly produces the end (the act willed by God).
If God wills to permit a person to resist His grace, He grants him a sufficient, and not an efficacious, grace.
An important question;
Way would God wills that we resist his grace?
Because sometimes He wills to permit us to do acts of sins for the reason to convert our sins into good, this is a part of the process the way God makes us saints.
As we see above, with the provisions of sufficient and efficacious graces God absolutely Governs/ controls the entire human race.
In the theory of Molinism there are only sufficient graces, if someone decide without God’s aids to cooperate with it his consent makes the grace efficacious.
As we see above, God has no control over the Molinists.
For a Molinist CCC 600 offered by God with a sufficient grace, if he choose he accepts it, if he choose he rejects it. – Heaven is a maybe, man’s fate (heaven or hell) is in himself.
For a Thomist CCC 600 offered by God with an efficacious grace which enlightens the mind and freely and infallible applying the will to choose the good and to act. – With efficacious graces Heaven is 100 % sure, man’s fate is in God.
Catholic Encyclopedia Divine Providence says.
Life everlasting promised to us, but unaided we can do nothing to gain it.
If we mix Thomism and Molinism together it causes us the greatest confusions.
Strictly speaking, if a Thomist ends up in hell his blood is in God’s hands, because his fate/ destiny is in God, if a Molinist ends up in hell his blood is in his own hands, because his fate/ destiny is in himself.