To worship God ‘in spirit and in truth’ is first and foremost a way of saying that we must worship God by means of Christ. In him the reality has dawned and the shadows are being swept away (Hebrews 8:13). Christian worship is new covenant worship; it is gospel-inspired worship; it is Christ-centered worship; it is cross-focused worship.
Worship by the Book (Grand Rapids, Mi.: Zondervan, 2002), 37
(HT: Of First Importance)