The difference between the free will of the blessed and that of other men is that the blessed have aligned their free will with God's, which is Fate. Thus, they are content wherever God places them because God's will is equivalent to Divine Justice. Another way of saying this is that the blessed have yielded to absolute will, which always acts for justice, and have purged all their contingent wills, which act for lesser things. The blessed therefore see their free will as "His most prized gift" to mankind. Vows, then, represent a surrender of one's free will to God and mean that one has placed himself at the hands of God's will.
God's so-called gift of free will to man is not as generous as Dante would lead us to believe; free will makes sin possible and thus can condemn some men to Hell.
By generously giving man free will, God still ensures that mankind has every chance of accessing Heaven; he gives everyone natural love and intact will.