Bread gained by deceit is sweet to a man,
but afterward his mouth will be full of gravel.
"Bread gained by deceit," in context with the previous proverb, is probably a reference to money or material possessions. Thus, deceitful bread refers to possessions gained by fraud. But bread can also be used to refer to sex as well. It is hard to miss the allusion of Woman Folly in 20:17. Deceitful bread in our text is quite similar to stolen water and secret bread in 9:17:
13 The woman Folly is loud;
she is seductive and knows nothing.
16 “Whoever is simple, let him turn in here!”
And to him who lacks sense she says,
17 “Stolen water is sweet,
and bread eaten in secret is pleasant.”
18 But he does not know that the dead are there,
that her guests are in the depths of Sheol. (Proverbs 9:13, 16-18)
Our proverb warns us that what looks like a sweet deal is actually a bad deal. Sin, by its nature, is deceptive. While it may taste good in the act, the problem is the after taste, which is poisonous. Just as Woman Folly's house is actually a place of death (9:18), so the sin that tastes sweet at first is actually a poison that kills its victims unless they see the truth and repent.
The word "afterward" in line two, is often translated in other verses as the word end (e. g., Proverbs 5:11, 14:12-13, 16:25, 20:21, 23:32, and many others). Proverbs, and this is true of the whole Bible, wants us to see that we must learn to judge things by their end, as God's Word shows us that end. As Kidner says, "nothing can be judged by its first stages." "The delicious ends as the disgusting; the soothing as the murderous."
Of course, the word end has two meanings, and both of these should be used in determining a wise course through life. End can refer to our purpose in life. "What is man's chief end/purpose?" The Westminster Shorter Catechism answers, "Man's chief end is to glorify God, and to enjoy him forever." If our end is to glorify God, how foolish we are to ignore and despise his instruction.
But end also can refer to our final destiny, which is either heaven or hell. If all things are going to be united in Christ (Ephesians 1:10), then it is the height of folly to live in ways that belie that truth here on earth. If Christ is the prize or goal of the Christian's upward calling, then we are foolish not to seek that end (Philippians 3:12-14). Like an athlete who focuses all his attention on winning the race, he trains with the end in mind (1 Corinthians 9:24-27; 2 Timothy 2:5).
One other illustration of the importance of living in accordance with our end is found in 2 Peter 1. There we are urged to not to be "nearsighted" (v. 9). A person who is nearsighted cannot see things far away. All he can see is what is close to him. Spiritually, this is our exact problem!
Proverbs is a book that urges us to pursue character, which is wisdom embodied. Our Lord Jesus Christ embodied the Father's wisdom perfectly. But this is the goal and end for all of God's adopted children, who have through faith in God's Son have been born into the family as well. 2 Peter 1 urges us to pursue a new character that fits the family likeness. To do so is to see the end:
3 His divine power has granted to us all things that pertain to life and godliness, through the knowledge of him who called us to his own glory and excellence, 4 by which he has granted to us his precious and very great promises, so that through them you may become partakers of the divine nature, having escaped from the corruption that is in the world because of sinful desire. 5 For this very reason, make every effort to supplement your faith with virtue, and virtue with knowledge, 6 and knowledge with self-control, and self-control with steadfastness, and steadfastness with godliness, 7 and godliness with brotherly affection, and brotherly affection with love. 8 For if these qualities are yours and are increasing, they keep you from being ineffective or unfruitful in the knowledge of our Lord Jesus Christ. 9 For whoever lacks these qualities is so nearsighted that he is blind, having forgotten that he was cleansed from his former sins. 10 Therefore, brothers, be all the more diligent to confirm your calling and election, for if you practice these qualities you will never fall.11 For in this way there will be richly provided for you an entrance into the eternal kingdom of our Lord and Savior Jesus Christ.