That's Calvinism's Catholic roots talking.
nahhh - it's found in the Bible. There are lots of mysteries unknown to mankind. Only God knows the end from the beginning. No one can understand the free will of man and the will of God and how they intersect. Rom 9 says clearly that God can force people to harden their hearts, because He is God and has done so for His purposes.
1 Timothy 3:16
And without controversy great is the mystery of godliness: God was manifest in the flesh, justified in the Spirit, seen of angels, preached unto the Gentiles, believed on in the world, received up into glory.
Deuteronomy 29:29
The secret things belong unto the Lord our God: but those things which are revealed belong unto us and to our children for ever, that we may do all the words of this law.
Isa 55
For my thoughts are not your thoughts,
neither are your ways my ways, saith the Lord.
9
For as the heavens are higher than the earth,
so are my ways higher than your ways,
and my thoughts than your thoughts.
10
For as the rain cometh down, and the snow from heaven,
and returneth not thither, but watereth the earth,
and maketh it bring forth and bud,
that it may give seed to the sower, and bread to the eater:
11
so shall my word be that goeth forth out of my mouth:
it shall not return unto me void,
but it shall accomplish that which I please,
and it shall prosper in the thing whereto I sent it.