Prophesying means delivering a special message from God, not just predicting the future (see 11:4–5; 13:2, 8; 14:1–25, 29–33; 1 Thessalonians 5:20; compare Acts 13:1–2; 21:4, 10–11).
The gift to discern if a message is from God's Spirit or another spirit is essential for any Christian community open to God's word (see 1 Corinthians 14:29; 1 Thessalonians 5:19–21; compare Acts 16:16–18; 1 John 4:1–3).
For Paul, speaking in unknown languages means using a spiritual language that needs the gift of interpretation to be understood. By ranking this gift lower (both here and in 1 Corinthians 12:28), Paul indicates that the gift of tongues is less important, as the Corinthian church had become overly fascinated with it (compare 13:1, 8; 14:1–25, 27).
The ability to interpret is not about translating with natural skill, but about spiritually understanding the Spirit's message through the gift of tongues (see 14:5, 13, 26–28).