Yea, my reins shall rejoice, when thy lips speak right things.
Fathers are very happy when sons are noble and wise, which is shown by sober and right speech, indicating a pure and righteous heart. Solomon exhorted his son to wisdom by telling him how much he would be pleased by his virtuous life (Pr 23:15-16). Sons must realize how important it is to their fathers for them to be prudent and virtuous in their lives. By honoring their fathers, such sons will also secure God's blessings (Eph 6:1-3).
The opening word of this proverb, "yea," connects it to the previous words. This term of agreement and explanation ties two verses together. Solomon had written, "My son, if thine heart be wise, my heart shall rejoice, even mine" (Pr 23:15). Solomon told his son how much it would mean to him for his son to be wise in heart and right in speech (Pr 23:15-16).
What were Solomon's reins? What are any father's reins? Most today think of reins as the leather straps or thongs attached to the bridle or bit on both sides of a horse's head and used by the rider or driver to control or direct the horse. Did Solomon mean these reins? If he did, how would they rejoice, if his son had a wise heart and right speech?
Thankfully, there is another definition for reins, which fits our proverb perfectly. "Reins" once meant the kidneys, and they became a metaphorical word indicating a man's inward desires and affections, very similar to the use of "heart." When combined together, heart and reins, they form a powerful metaphor for all the inward parts of a man.
Compare this proverb with the one before it. Solomon first said his heart would rejoice, which we understand clearly as the seat of his affections (Pr 23:15). Then he said his reins would rejoice, which we must understand in the same way, as a word describing inward thoughts and feelings (Pr 23:16). A wise son brings inward pleasure to heart and reins.
Scripture uses "reins" only for kidneys and the inward affections and desires; it does not use the term for the leather straps used to guide a horse (Job 16:13; 19:27; Ps 7:9; 16:7; 26:2; 73:21; 139:13; Isaiah 11:5; Jer 11:20; 12:2; 17:10; 20:12; Lam 3:13; Rev 2:23).
What can a son do to cause his father's reins - his soul, heart, desires, and affections - to rejoice? He can speak right things. Foolishness is bound in the hearts of young men, and it often comes out through their lips. When a son speaks carefully, prudently, and wisely, a father is warmed on the inside, for he knows his son is ruling his heart and tongue.
Speech is a great indicator of character. Fools give themselves away quickly by their ungoverned and idiotic speech (Pr 15:2,28; 18:6-7; Eccl 10:12-14). Wise sons are gracious in speech (Pr 22:11; Eccl 10:12; Col 4:6). They rule their tongues, which indicates great temperance and prudence (Jas 3:2-12). They speak the truth in love (Eph 4:15).
How does a father know if he has a great son? He listens for wise and righteous speech, kind and helpful words, and faithful and true testimony. He listens for prudent answers, and he wants to kiss his son when he hears them (Pr 24:26; 25:11). A father knows that good speech reveals a good heart (Matt 12:35). He perceives the future good his son will do.
Sons cause fathers joy or grief. A wise son is a great blessing and rejoices his father, but a foolish son is a calamity and causes him much pain (Pr 10:1; 15:20; 17:21,25; 19:23; 23:24-25; 29:3). God ordained fathers, and He rewards or punishes sons, depending on the joy or sorrow they cause their fathers (Eph 6:1-3). Foolish sons grieve their fathers and earn God's judgment; wise sons thrill their fathers and earn God's blessing.
Jesus of Nazareth was the perfect son. He was subject to Joseph and His mother, and He grew in wisdom and pleased both God and men (Luke 2:51-52). What happy parents! He always spoke right things, as both friends and enemies marveled at His control of His tongue (Matt 22:22; 27:14; John 7:15,46). He always pleased His Father in heaven, Who rewarded Him with the throne of the universe (John 8:29; Phil 2:5-11; Heb 1:8-9).