Acts 9:3 is not a good example at all. if you read further, the Lord sent Ananias ( the Church ) to Saul and in 22:16 he tells Saul to be baptized and wash away his sins.
even in Acts 8 where the eunuch is reading the Scriptures, the Holy Spirit sends Philip ( the Church ) to him to explain what he is reading to him, proclaim Jesus Christ to him and finally baptize him.
-apparently- you want to make the Church something less than the Body of Christ on earth. it is the Church that Jesus gave His authority to to teach and baptize. the Church is a type of sacrament as it the instrument the Holy Spirit uses to preach the Word and administer the sacraments.
your constant use of the “plain meaning of Scripture” would get heated arguements from Baptists for example and many other Protestants when discussing baptism and the Lords Supper. ( Lutherans are very close to Catholics in these areas, i know, my wife is Lutheran. sometimes if i close my eyes, i think i am at a Catholic Mass when i attend services with her ) but the very existence of so many denominations and sects shows your “plain” meaning aint so “plain” to a lot of folk.
Jesus prayed in John 17 that His followers be one, so the world would believe He was sent by the Father. Paul tells us in Ephesians there is One Lord, One Faith, One Baptism.
may all Christians pray about the implications of this truth.
My dear one Lord one faith one baptism, first, give your wife a hug from me. It must be that not only is she still Lutheran, but that she recognizes that you are a Christian, and can live with you ... and you with her. That’s pretty cool. Second, notice that before you said, “Acts 9:3 is not a good example at all.”, I already acknowledged, “Well, Acts 9:3ff comes to mind. However, that is hardly the point.” OK?
The “very existence of so many denominations and sects” speaks not so much to the lack of the clarity of the Scriptures as to the power of the devil and the fallenness of humanity. Scripture is plain. Could God be true and that not be so? The problem is that the heart and mind of man is darkened. This is the effect of original sin. This observation would be completely in line with the plain - repeat - plain sense of the Scriptures. As to what you say thereafter, rest assured I am very well aware of my differences - Lutheran differences - with Baptist theology ... differences that will never go away, as long as they remain Baptist in theology.
But my final point is simply this: God’s written word, Old and New Testament, is not and never will be at variance with the preaching and teaching of His church, who is charged with conveying His word to mankind. That is why, as Peter - Peter! - said, “If anyone speaks, let him speak as the oracles of God.” Let the church speak as its Lord speaks. For the Lord alone is Lord and Savior of the church. She depends on Him, not the other way around. She is the bride, He the bridegroom. That is Peter’s point. It is the bottom line, the final deal, the end of the line, the buck stops here, kind of thing. The bridegroom and bride are one, vz. Ephesians 5 and 1 Peter 3, and the bridegroom is the head. The bride speaks the mind of the bridegroom. The bride does not determine the mind of the bridegroom. She listens. She agrees. She consents. For He and He alone is Lord and Savior. She is the one who is saved.
That is my point. The rest is jargon.