Were the New Testament writers aware that their writings were inspired by God The Holy Spirit and therefore authoritative?
Yes. In 1st Corinthians 2:13 the apostle Paul said he spoke “not in words taught us by human wisdom but in words taught by the Spirit, expressing spiritual truths in spiritual words.” In this passage Paul (who wrote over half the New Testament) affirmed that his words were authoritative because they were rooted not in fallible men but infallible God The Holy Spirit. Remember The Holy Spirit of truth was promised to the apostles to teach and guide them into all the truth (see John 16:13).