CathInfo.com

I forgot to bold a section of what was quoted previously.


https://www.cathinfo.com/crisis-in-the-church/rr-why-don't-you-get-behind-father-chazal's-sede-impoundism/msg886368/#msg886368

This may be more clear from the following: If a person who has come to the use of reason and professes heresy at the time of his baptism, he is indeed indelibly marked as a Christian, but he is not sanctified—the other supernatural effects of baptism being suspended for want of the proper dispositions or preparations which are required to receive not only the sacrament, but also its supernatural effects. One of the most essential requisites to receive these effects is to have the true faith, i.e., to believe God, speaking through the Catholic Church. Now heresy, material heresy not excepted, is a want of this faith, on account of which the supernatural effects of baptism are suspended. God cannot unite himself with a soul that lives in heresy, even though it be only material heresy. As the supernatural sanctifying effects in this case are suspended, so they are for the same reason, destroyed in him who was baptized in his infancy and became a heretic, though only a material heretic, when he came to the use of reason. This person, to be again reconciled with God, must renounce heresy, believe the Catholic Church, and receive worthily the sacrament of penance; or if this cannot be had, he must have perfect contrition or charity with the desire (at least implicit) to receive the sacrament of penance. The other person, however, will be reconciled with God and truly sanctified, as soon as he renounces heresy, believes the Catholic Church, and has at least attrition (imperfect supernatural sorrow) for his sins, because it is then that the supernatural sanctifying effects of baptism take place. It is therefore evident that, if these persons and others like them were to die in heresy, they would be lost forever. (See Theolog. Curs. Compl. De Confirmatione, Part II., Q. II., art. vi.)

Sean's been given the answer multiple times, he keeps asking because he does not like the answer.

Correct.

Probably the same thing I don’t get about how I can lose grace by committing a mortal without the requisite full knowledge.

This is just the error of rationalism, since you are denying that one in the state of grace has a working conscience, a guardian angel, and the Holy Ghost's inspirations.  St John tells us in John 1:9...That was the true light (Christ), which enlighteneth every man that cometh into this world. 

If all men (baptized and unbaptized) are enlightened by God when they are born, how much moreso, is one enlightened who is baptized and in the state of grace?  Infinitely more.

One saint said that it could be a mortal sin if one did not say any prayers for a month.  Isn't it also a mortal sin for one to miss Mass on Sundays/Holy Days?  Even for a protestant, if they don't go to church, that's a mortal sin against the natural law and the 3rd commandment.

Children even as young as 3 can understand spiritual things, like guardian angels and God, etc.  One who has reached the age of reason has a DUTY to do the basics (pray, attend church).  If not, that's a mortal sin.

To say that God does not prompt all human beings to follow Him, to know Him, to worship Him is pure rationalism, naturalism and a denial of God's laws.  If He sought fit to create such laws, then He will give everyone an opportunity to follow them.  God does not command the impossible.  God gives everyone a choice in this life.  For there to be a choice, there must first be knowledge of what one is choosing - God vs not-God.  And He infallibly gives everyone such a knowledge because He wants them to choose.