Matthew 5:8

οἱ καθαροὶ τῇ καρδίᾳ : τ. καρδ. may be an explanatory addition to indicate the region in which purity shows itself. That purity is in the heart, the seat of thought, desire, motive, not in the outward act, goes without saying from Christ's point of view. Blessed the pure. Here there is a wide range of suggestion. The pure may be the spotless or faultless in general; the continent with special reference to sexual indulgence those whose very thoughts are clean; or the pure in motive, the single-minded, the men who seek the kingdom as the summum bonum with undivided heart. The last is the most relevant to the general connection and the most deserving to be insisted on. In the words of Augustine, the mundum cor is above all the simplex cor. Moral simplicity is the cardinal demand in Christ's ethics. The man who has attained to it is in His view perfect (Matthew 19:21). Without it a large numerical list of virtues and good habits goes for nothing. With it character, however faulty in temper or otherwise, is ennobled and redeemed. τὸν θεὸν ὄψονται : their reward is the beatific vision. Some think the reference is not to the faculty of clear vision but to the rare privilege of seeing the face of the Great King (so Fritzsche and Schanz). “The expression has its origin in the ways of eastern monarchs, who rarely show themselves in public, so that only the most intimate circle behold the royal countenance” (Schanz) = the pure have access to the all but inaccessible. This idea does not seem to harmonise with Christ's general way of conceiving God. On the other hand, it was His habit to insist on the connection between clear vision and moral simplioity; to teach that it is the single eye that is full of light (Matthew 6:22). It is true that the pure shall have access to God's presence, but the truth to be insisted on in connection with this Beatitude is that through purity, singleness of mind, they are qualified for seeing, knowing, truly conceiving God and all that relates to the moral universe. It is the pure in heart who are able to see and say that “truly God is good” (Psalms 73:1) and rightly to interpret the whole phenomena of life in relation to Providence. They shall see, says Jesus casting His thought into eschatological form, but He means the pure are the men who see; the double-minded, the two-souled (δίψυχος, James 1:8) man is blind. Theophylact illustrates the connection between purity and vision thus: ὥσπερ γὰρ τὸ κάτοπτρον, ἐὰν ᾖ καθαρὸγ τότε δέχεται τὰς ἐμφάσεις, οὕτω καὶ ἡ καθαρὰ ψυχὴ δέχεται ὄψιν θεοῦ.