Bear in mind that the Pope had been teaching systematically on this subject for over a year at this point; there’s a lot that’s assumed in his use of words. I don’t think he would disagree that we should regard the heart (especially if you mean the way we can be led by our emotions to disregard reason) as always capable of deceit. In fact, that’s what he was just teaching, wasn’t it? But I think he was trying to caution us against taking an opposite extreme position of regarding real human relational responses–trust, awe, tenderness, concern, desire, joy–as “really” something else. Bear in mind that when he teaches he has to have in view not only certain conservative extremes (like regarding all human good as masked human evil) but also certain liberal extremes (like regarding all human good as expressions of economically dominant cultures oppressing the weak).

And, after all, even if I must guard against the deception by which lust masquerades as love (isn’t that the sort of thing Jeremiah has in mind?), I certainly cannot “love [my] wife as Christ loved the Church” if I do not believe Christ’s human heart, and mine, can be moved to just such love.