How do we know that the Gospel of Luke is inspired?

Luke asserts that he 'had perfect understanding of all things from the very first,' indicating that his writings were based on careful research. However, the true authority of Luke's Gospel lies in the doctrine of plenary inspiration, where every word is believed to be guided by the Holy Spirit. This belief affirms that Luke wrote not merely as a man but as a vessel of divine revelation. Thus, the Gospels, including Luke's account, are considered the 'word of God' and are to be accepted as fully authoritative in guiding the faith of believers.