2Tim 3:15 and that from childhood you have known the Holy Scriptures, which are able to make you wise for salvation through faith which is in Christ Jesus
The sufficiency of scripture prepares man for salvation, and three examples come to mind. Timothy as Paul reminds him did not come through any other means but by the truth of the scripture (knowledge of the word made him wise in preparation for salvation). Cornelius (Acts 10) received a vision, an angel delivered good tidings message of God’s acceptance of his alms and prayers. Rather than God by the angel declare him saved sent Peter to preach Jesus (gospel) to him and his household. An Ethiopian eunuch’s heart became tender as he was reading Isaiah (Acts 8) and God by an angel sent Phillip to meet him, Acts 8:30-32, “30 So Philip ran to him, and heard him reading the prophet Isaiah, and said, “Do you understand what you are reading? 31 And he said, “How can I, unless someone guides me?” …35 Then Philip opened his mouth, and beginning at this Scripture, preached Jesus to him”.
In these three examples we see the use of scripture to preach the gospel, it prepares one for salvation. The understanding is informed by the word of God, faith comes by hearing, hearing the word of God.