After this Dante comes to a discussion of Love, which is here both a quality and an act conditioned by that quality: 'Love is nothing else than the spiritual union of the soul with the object loved.' 'And since the constitution of the divine nature is shown in the excellences of nature, therefore the human soul unites herself spiritually with them the quicker and the closer as they themselves appear more perfect' (III, ii). And 'this lady' exhibits the pattern of man's essence as it exists in the divine mind (III, vi). This is to repeat formally what has been asserted often enough in the Vita to be seen in Beatrice. She is the heavenly norm; she is what everyone ought to be; 'she is as completely perfect as the essence of man can possibly be.' There is nothing new or uncommon about this experience; it is in a great many novels and films and plays and songs; our modern songs hold it as much as the lyrics of the metaphysicals. All that is new is the seriousness with which Dante treats it and the style in which he expresses it. The lady creates in her lover the sensation of supreme content. It does not last. Why not? Dante, at least, had a perfectly definite answer (III, vi). Everything desires its own perfection: 'in this all desires are appeased and for the sake of this all is desired.' This desire causes every delight to lack something, 'for there is in this life no delight so great as to assuage our souls' thirst, so that this longing for our own perfection is not always in one thought.' Our desires are everlasting, and to see an image of perfection is not the same thing as to be perfect ourselves, which until we all are, possession, even the possession of Beatrice, must lack perfection. This is what all the talk of 'the ideal' comes to; the ideal can never satisfy us until we are ideal. He who pursues any hope of satisfaction without his own conditioning perfection is bound, sooner or later, straight for the Inferno. [emphases mine]
The above is from The Figure of Beatrice. There is more of Williams' exposition of sanctifying grace -- demonstrated in his poetry -- in Taliessin Through Logres and The Region of the Summer Stars.
I think Wesley would approve of Williams. Wesley's own theology emphasized that perfection, for the Christian, can only be perfection in love, and that love was the experience of heaven in the here and now. To love perfectly requires us first to know and love what is perfectly loveable; that experience changes us, and we reach perfection in love when we are so changed as to begin to love perfectly what is not perfectly loveable, for that is what God in Christ did for us.
Williams and Dante are both poets, but they are not merely poets. And they are both better at explaining holiness than most theologians.