By saying, with all thy mind, he does not admit of any division of love to other things, for whatever love you cast on lower things necessarily takes away from the whole. For as a vessel full of liquid, whatever flows therefrom must so much diminish its fulness; so also the soul, whatever love it has wasted upon things unlawful, has so much lessened its love to God.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: in Ps. 44.