Dear brothers and sisters in Christ,
"God is spirit, and those who worship him must worship in spirit and truth" (John 4:24).
Let's ask the Lutheran question. What does this mean?
To worship God in spirit is to receive the gifts His good gifts in faith. While we bring our sin to worship, and therefore begin by confessing this sin, God brings His gifts: Forgiveness of sins, Life, and Salvation. To worship God in spirit, then, is to worship in what the Holy Spirit gives, and that is faith. Faith is what clings to the gifts of God in Christ Jesus. When these gifts are bestowed in the Holy Absolution and Preaching of the Gospel and in the administration of the Sacraments, faith says "Amen! This is true. I am forgiven, and have life in Jesus Christ. Thanks be to God." This is to what it means to worship in spirit.
So what about truth?
In the 17th chapter of John, we read these words: "Sanctify them in the truth; your word is truth" (verse 17). In other words, to worship in truth is to have your worship be based on, and flow from the Word of God. Our worship is not based on man-made innovations, or a preachers hobby horse. Our worship is true when the Gospel is preached in its truth and purity, and the Sacraments are administered in accord with Christ's command. We worship the way we do because of the truth(s) our worship confesses. It's Christ-centered, cross-focused. It proclaims both the Law and Gospel. We sing psalms and spiritual songs that clearly confess the faith that trusts in Christ alone. Because the Church's one foundation, is Jesus Christ her Lord, and apart from the truth of God's Word, we don't receive the blessings, and are therefore, not able to worship in spirit or in truth.
Worship in spirit and in truth. Say yes to the promises of God in Christ Jesus, for they are the truth that sets you free. Amen.