“But these speak evil of those things which they know not: but what they know naturally, as brute beasts, in those things they corrupt themselves.” (Jude 1:10)
Both Jude and Peter use essentially the same terms when they speak of people who are like “brute beasts” (2 Peter 2:12). Both use the qualifying adjective “natural” to draw a precise distinction between those who are only alive physically and those who have been given eternal life by the Spirit of God.
Prior to being twice-born, all men are “by nature the children of wrath” (Ephesians 2:3) and have not yet been given “the divine nature, having escaped the corruption that is in the world through lust” (2 Peter 1:4). Such “natural” people are “sensual, having not the Spirit” (Jude 1:19) and therefore cannot receive “the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned” (1 Corinthians 2:14).
These strong pictures are not incidental for understanding the challenge to “earnestly contend for the faith which was once delivered unto the saints” (Jude 1:3). Jude and Peter are describing the intransigence of those who resist the truth—especially of the “tares” who have been planted by the Enemy among the “wheat” in the Lord’s field (Matthew 13:24-30).
The Greek term translated “brute” by both Jude and Peter is a combination of the negative particle a and the basic word for intelligent communication, logos. We must therefore expect the resistance to take form “without reason.” The unsaved cannot understand God’s message without the transformation of the new birth. Their efforts to undermine “the faith” will always be based on human (natural) reasoning.