Except that Jesus himself told us that understanding the mysteries of the kingdom is a gift from God:
Matthew 11:25,26
Matthew 13:11
Matthew 16:17
Mark 4:11
Luke 8:10
This is also stated elsewhere in both the OT and NT:1 Corinthians 2:10-14, Romans 16:25-26, Colossians 1:26-27, Ephesians 3:3-5, 1 John 2:20-21, Daniel 2:22, Isaiah 6:9-10, Deuteronomy 29:4, Jeremiah 33:3, Proverbs 1:23, Amos 3:7, Psalm 25:14, etc . . .
The enlightenment of faith IS a gift from God the Holy Spirit through the word. Without this gift, nobody could believe.
But through this gift, anyone can believe. That is why the parable says that it is not the Sower or the seed that is the problem. It is the soil.
And, just to point out using your own words, this is a GIFT from God. A gift is freely given and freely accepted - or refused. But this goes against another tenet of Calvinism - the irresistible grace to the chosen elect. This too is not scriptural, but even Calvinist defenders like yourself are not immune from the truth of scripture.