Romans 15:14

Paul’s knowledge of the church in Rome had come to him through sources other than personal observation (Romans 15:22-24).

"Goodness" is moral excellence that comes through the working of God’s Spirit (Galatians 5:22; cf. Romans 6:13). Goodness is necessary to apply the truth to life, as is knowledge. This was primarily a self-taught church (Romans 6:17), and the believers were able to instruct one another. "Admonish" or "instruct" means to inculcate (cf. Colossians 3:16; 1 Thessalonians 5:14).

"Morally, they were ’full of goodness,’ intellectually they were ’complete in knowledge,’ and functionally they were ’competent to instruct one another.’" [Note: Mounce, p. 266.]