As I understand it, WELS teaches that there must be complete doctrinal unity before any kind of joint Christian activity can take place amongst believers. And yet when I read your proof passages they all seem to be related to the key teaching of Scripture -- justification by faith alone in Christ alone. Isn't it impossible on this side of heaven to be "in perfect agreement?" It seems like WELS would say that if we agree on everything except who we identify as the Antichrist, we can't pray together. Yet, in Philippians 3:15-16, Paul seems to imply that there is room for disagreement on non-fundamental teachings yet still be together.
The “Church and Ministry” section of This We Believe, a statement of belief of our church body, explains what we teach and profess about doctrinal unity and fellowship.
“We believe that God directs believers to acknowledge oneness in faith with Christians whose confession of faith submits to all the teachings of Scripture (John 8:31; 1 Thessalonians 5:21,22). We believe, furthermore, that individuals through their membership in a church body commit themselves to the doctrine and practice of that church. To assert that unity exists where there is no agreement in confession is to presume to look into people’s hearts. Only God can look into people’s hearts. It is not necessary that all Christians agree on matters of church ritual or organization. About these the New Testament gives no commands (Romans 14:17).
“We believe that those who confession of faith reveals that they are united in the doctrines of Scripture will express their fellowship in Christ as occasion permits (Ephesians 4:3). They may express their fellowship by joint worship, by joint proclamation of the gospel, by joining in Holy Communion, by joint prayer, and by joint church work. God directs believers not to practice religious fellowship with those whose confession and actions reveal that they teach, tolerate, support, or defend error (2 John 10,11). When error appears in the church, Christians will try to preserve their fellowship by patiently admonishing the offenders, in the hope that they will turn from their error (2 Timothy 2:25,26; Titus 3:10). But the Lord commands believers not to practice church fellowship with people who persist in teaching or adhering to beliefs that are false (Romans 16:17,18).”
As indicated, the Scripture passages used to explain what we teach and profess about doctrinal unity and fellowship are not limited to the subject of justification by faith alone in Christ alone.
When it comes to Philippians 3:15-16, the phrase “such a view of things” in verse fifteen takes us back to the previous verses where the apostle Paul was speaking of zealousness in living the Christian life not classifying doctrines of the Bible.
Unity in the faith is a precious gift of God the Holy Spirit. We thank him for it. We seek to preserve it. We look for greater expressions of it.