Acts 2:42 says the believers in the early church "were continually devoting themselves to the apostles' teaching." The church needs God's truth as delivered to us through His apostles, which means consistent teaching from the Bible, both the Old and New Testaments. The teacher has no authority in and of himself, but he does have God's Word, which is authoritative. Paul told Timothy to "command and teach" the Scriptures (1 Timothy 4:11), and he told Titus to "Declare these things; exhort and rebuke with all authority" (Titus 2:15). Instruction, whether public or private (including preaching, teaching, counseling, and discipling), is authoritative only in so far as it is biblical.
God's word can only truly be received in humility. James 1:21 says to "put away all filthiness and rampant wickedness and receive with meekness [humility] the implanted word..." That means that we don't just listen to and agree with God's word, but submit to its authority in our lives and apply it by faith — trusting it to change us for our good as we obey. Paul said to the Thessalonians, "And we also thank God constantly for this, that when you received the word of God, which you heard from us, you accepted it not as the word of men but as what it really is, the word of God, which is at work in you believers" (1 Thessalonians 2:13).