Thomas Aquinas, on Heb 12:15

“Looking diligently, lest any man be wanting to the grace of God; lest any root of bitterness springing up do hinder, and by it many be defiled.”

“688 (cont.). – In regard to the second loss, namely, of God's grace in the present he says, see to it that no one fail to obtain the grace of God. For grace is lost by discord and uncleanness: 'He is not a God of dissension, but of peace' (1 Cor. 4:33); 'His place was made in peace' (Ps. 75:3); 'Your eyes are too pure to behold evil; and you cannot look on iniquity' (Hab. 1:13); 'The Holy Spirit of discipline will flee from the deceitful… He shall not abide when iniquity comes in' (Wis. 1:5). But the Apostle is speaking figuratively. For grace is not obtained by merit; otherwise, grace would not be grace. Yet a man must do what he can. But God in His most generous will gives it to all who prepare themselves: 'Behold, I stand at the door and knock. If any man open to me, I will come in to him' (Rev. 3:20); 'He will that all men be saved' (1 Tim. 2:4). Therefore, God's grace is not wanting to any one, but it communicates itself to all, as far as it is concerned, just as the sun is not wanting to the eyes of the blind. He says, therefore: see that no one fail to obtain the grace of God. 689. – But on the other hand: if grace is not given because of works, but only by the fact that a person places no obstacle, it seems to follow that the possession of grace depends solely on free will and not on God's choice. This is Pelagius's error. I answer that the very fact that a person places no obstacle is due to grace. Hence, if anyone places an obstacle and his heart is moved to remove it, this is due to the gift of God's grace calling by His mercy: 'But when it pleased him who separated me from my mother's womb and called me by his grace' (Gal. 1:15). But this gift of grace is not sanctifying grace. Therefore, the fact that a person removes that obstacle is owing to God's mercy; if it is not removed, it is owing to God's justice. But he does not say, 'lest you fail,' but lest anyone fail, because everyone should be solicitous for his neighbor: 'He gave everyone commandment concerning his neighbor' (Sir. 17:12). 690. – Then (v. 15b) he comes specifically to advising the avoidance of sins contrary to each of the aforesaid medicines: first, he advises them to avoid sins contrary to peace; secondly, contrary to holiness (v. 16). 691. – He says, therefore, that no root of bitterness spring up and cause trouble. That is bitter which cannot be tasted without disgust. Therefore, a person's conversation is said to be bitter when it cannot be without offending those with whom he lives. Against this it is said of wisdom: 'Her conversation has no bitterness, nor her company any tediousness, but joy and gladness' (Wis. 8:16). Therefore, one knows how to live in wisdom, when his conversation is not bitter. This happens when his words and deeds are not harsh. Hence he says, that no root of bitterness spring up and cause trouble, i.e., bitterness gradually begun and rooted in the heart, springing up to cause trouble [hinder peace] and consequently, grace and the vision of God: 'Lest there should be among you a root bringing forth gall and bitterness' (Deut 29:18): 'Ephraim has provoked me to wrath with his bitterness' (Hos 12:14). Or the root of bitterness is an evil thought of harmful pleasure, which springs up when by consent one accomplishes the deed. And by it many become defiled, because not only the one in whom it exists but others also are defiled by his example: 'A little leaven corrupts the whole lump' (1 Cor. 5:6).”

Imported from an open dataset — not yet checked against the printed edition.