Wise in Heart 5 Aug 2020
The wise in heart will be called intelligent.
Sweetness of speech increases knowledge.
Intelligence is not a requirement for wisdom. Some simple (not learned) people respond usually with wisdom.
Sweetness of speech may be abused easily.
Other bible translations may say: "The wise heart will be called discerning." Which may show the working of the Holy Spirit. Usually it brings forth peace, love and other good fruits. Any initially good gift can be abused, even love.
About the second part. Some good teachers may have a gift of language. They are capable to wrap knowledge in beautiful words. Some famous philosophers and theologians have a gift for teaching in pleasant language.
A Careful Conclusion
Proverbs 16:21 may teach about the working of the Holy Spirit. Typically wrapping wisdom in beautiful language is not a natural gift from birth. Some people develop it little by little. For me such a gift feels godly.