The similitude in Grace Abounding that Bunyan observed between clean and unclean beasts and professing Christians is both striking and insightful:
71. I was almost made, about this time, to see something concerning the beasts that Moses counted clean and unclean. I thought those beasts were types of men; the clean, types of them that were the people of God; but the unclean, types of such as were the children of the wicked one. Now, I read that the clean beasts chewed the cud; that is, thought I, they show us we must feed upon the Word of God. They also parted the hoof; I thought that signified we must part, if we would be saved, with the ways of ungodly men. And also, in further reading about them I found that though we did chew the cud as the hare, yet if we walked with claws like a dog, or if we did part the hoof like the swine, yet if we did not chew the cud as the sheep, we were still, for all that, but unclean; for I thought the hare to be a type of those that talk of the Word, yet walk in the ways of sin; and that the swine was like him that parted with his outward pollutions, but still wanteth the Word of faith, without which there could be no way of salvation, let a man be never so devout (Deut. 14). After this I found, by reading the Word, that those that must be glorified with Christ in another world must be called by Him here; called to the partaking of a share in His Word and righteousness, and to the comforts and first fruits of His Spirit, and to a peculiar interest in all those heavenly things which do indeed fore fit the soul for that rest and house of glory which is in heaven above.
In some Reformed circles today it is fashionable to refer to sanctification as nothing more than getting used to one’s justification. To be an authentic Christian, you need to be in realistic about your sinfulness, and where sin abounds, it is said that grace does much more abound. This type of lifestyle, void of personal holiness but reveling in doctrinal precision, falls into Bunyan’s unclean category of those who chew the cud (feed upon the Word of God) but do not part the hoof (walk in the ways of sin).
The other situation may be found where the doctrines of grace are not so prominent. Someone may be very faithful in church attendance and outwardly righteous (parting the hoof) but yet have no delight or faith in the Lord and in the end wind up seeking to be justified by personal merit (not chewing the cud).
Both situations share a common assessment: they are an abomination to the Lord (Deut. 14:3), because they are not of faith. Saving faith is active, efficacious, and unfailingly evident, as expressed in the Westminster Confession of Faith, chapter 14:
1. The grace of faith, whereby the elect are enabled to believe to the saving of their souls, (Heb. 10:39) is the work of the Spirit of Christ in their hearts, (2 Cor. 4:13, Eph. 1:17–19, Eph. 2:8) and is ordinarily wrought by the ministry of the Word, (Rom. 10:14,17) by which also, and by the administration of the sacraments, and prayer, it is increased and strengthened. (1 Pet. 2:2, Acts 20:32, Rom. 4:11, Luke 17:5, Rom. 1:16–17)
2. By this faith, a Christian believeth to be true whatsoever is revealed in the Word, for the authority of God Himself speaking therein; (John 4:42, 1 Thess. 2:13, 1 John 5:10, Acts 24:14) and acteth differently upon that which each particular passage thereof containeth; yielding obedience to the commands, (Rom. 16:26) trembling at the threatenings, (Isa. 66:2) and embracing the promises of God for this life, and that which is to come. (Heb. 11:13, 1 Tim. 4:8) But the principal acts of saving faith are accepting, receiving, and resting upon Christ alone for justification, sanctification, and eternal life, by virtue of the covenant of grace. (John 1:12, Acts 16:31, Gal. 2:20, Acts 15:11)
3. This faith is different in degrees, weak or strong; (Heb. 5:13–14, Rom. 4:19–20, Matt. 6:30, Matt. 8:10) may be often and many ways assailed, and weakened, but gets the victory: (Luke 22:31–32, Eph. 6:16, 1 John 5:4–5) growing up in many to the attainment of a full assurance, through Christ, (Heb. 6:11–12, Heb. 10:22) who is both the author and finisher of our faith. (Heb. 12:2)