WCF 7.6 Under the gospel, when Christ, the substance, was exhibited, the ordinances in which this covenant is dispensed are the preaching of the Word, and the administration of the sacraments of baptism and the Lord's Supper: which, though fewer in number, and administered with more simplicity, and less outward glory, yet, in them, it is held forth in more fullness, evidence and spiritual efficacy, to all nations, both Jews and Gentiles; and is called the new testament. There are not therefore two covenants of grace, differing in substance, but one and the same, under various dispensations.
There is a gospel (new testament) principle of simplicity at the core of what Christ's finished work has done to our worship.
The Priest is now in heaven. The sacrifice has been performed once for all. He sings through His people's mouths and accompanies it by His work in the heart. His blessing is proclaimed by preaching, and in His royal-priesthood's admonishing one another in song and showing forth His death until He comes.
The very simplicity of the Christian worship assembly's liturgy announces, "the substance of these things is not so much here as it is in glory, where we are seated with Him, and where He presents us, and from where He preaches and He sings and He gives us Himself!" (cf. Heb 2:10–13, Eph 2:4–10)
Whatever extra formality is added upon earth mutes this announcement and obscures this reality. When we worship in simplicity and purity, we are not exulting in simplicity and purity but rather exulting in God through Christ. If, lacking the Spirit-given faith to perceive Him, we attempt to dress things up with that which we think will better present Him to ourselves, we unwittingly muddle the very means by which the Spirit is ordinarily pleased to give that faith.
When once God deemed it good to give Himself through the voice on the mountain as fleshed out by the inscripturated pattern given to Moses, His people frequently thought this might be enhanced by various locations and images, which came to be enshrined in their traditions. But God said that doing so is to "hate Him," and indeed He hated their worship (cf. Deu 4–5). They could only have the true God by way of the given worship.
Now, God has deemed it good to give Himself through the finished work of His only-begotten Son, personally led by the God-Man from the throne of glory and grace. The true "worship war" is not so much among varying preferences of men as it is between the gospel simplicity in which Christ is held forth and whatever hiding of Him from true Spiritual view comes by man's sophomoric (indeed, idolatrous) additions to that simplicity.