“Keep the message straight, Missouri! Get the message out, Missouri!"
— A.L. Barry, President, LCMS (1992-2001)

RE (from the article): “The modern use of ‘mission’ arose in the 19th century and was used to describe foreign evangelistic activity.”

The online Merriam-Webster’s dictionary dates the earliest known use of the English word “mission” to 1530, when it meant “the act or an instance of sending.” And the English word comes from the Latin word mittere that appears in many places in the Latin translation of the Bible that was completed by AD 405.

Forms of that Latin word are easily spotted in Scripture. In John 17:18, for example:
• English (ESV): “As you sent me into the world, so I have sent them into the world.”
• Latin (Vulgate.org): sicut me misisti in mundum et ego misi eos in mundum

So for more than 16 centuries, evidently, the English word “mission” or its Latin precursors have been used to describe someone being sent to another place to convey a divine message or complete a divinely assigned task.

RE: [“The word ‘mission’] came to refer to everything the church was supposed to be doing outside the church walls.”

Not necessarily. The meaning today varies with context. We understand the mission field to lie beyond our gatherings as believers. Yet the typical congregational mission statement describes the congregation's aims both inside and outside the church walls. The stated mission of the LCMS itself “is vigorously to make known the love of Christ by word and deed within our churches, communities and the world.”

RE: “If the people of God are not …, then they have nothing to share with the world.”

Nothing at all? How is it even possible to be "the people of God" and yet have "nothing to share with the world" (1 Peter 2:9)? Must the routine receipt of all the sacraments with a certain understanding occur before a believer can say anything to other people about the meaning of salvation in Christ? Surely someone who has obtained even a fundamental grasp of the atoning work of Christ might very well be enabled by the Spirit to declare, “We have found the Messiah!” (John 1:41) or “Jesus is Lord!” (1 Cor. 12:3). “The wind blows where it wishes” (John 3:8). And if God wishes, He can even make mindless, soulless stones acclaim Christ before the world (Luke 19:40)!

RE: “[E]very action of God through His church is directed toward the redemption and salvation of sinners.”

Does God not act through His church to address to the quality of people's lives on earth — guiding and equipping His children to be a blessing to others and thereby fulfill the purposes in this life for which He has shown mercy and still gives His gifts (Titus 2:14, 2 Cor. 5:15)? When Jesus said, “These things I have spoken to you, that my joy may be in you, and that your joy may be full” (John 15:11), wasn’t He speaking of a joy obtainable here and now?