Matthew Poole and continuators on Proverbs 27:19

19 As in water face answereth to face, so the heart of man to man .

The sense is either 1. As the image of a mans Face in the water answers to his natural Face who looks into it, or, as in water one mans face is like anothers, the difference of mens faces being not there visible, so one man resembles another, either in the temper of his Mind or Body, in which many men are alike one to another; or in the corruption of his Nature, in which all are alike. Or 2. As a man may see his own face if he look into the water, which is Natures Looking-Glass, or into any other Looking-Glass, so a man may discern his own Heart if he look into those Glasses whereby it discovers itself, if he examine his Thoughts and Inclinations, together with the general course of his Actions. Or 3▪ As the Face of a man standing by the waters is visible, not only to himself, but to others, by the shadow or image of it in the waters, so the Heart of a man is in some measure discernable, not only to himself, but to others also, who observe his disposition and carriage.