I don't see that anywhere in the NT -- although it wouldn't surprise me if you see things I don't see, and I see things you don't see. Like when my husband calls me into the kitchen and says, "Look in the fridge and see if you can see the mayonnaise." And I say, "OK, but first could you look next to the bed and find my glasses?" :o)
Perhaps you could provide me with the texts where it says baptism and communion are "declarations"?
The Christian faith is centered around the Incarnation, in and through which Christ our God is constantly working in and through physical, material, and sensory things. It is Christianity's rival, Gnosticism, which taught the false, hyperspiritual view that God disdained material things and that humans should defocus and disregard the body and physical things generally, in favor of disembodied spirituality.
Why did Christ use physical things? Why did He use spittle, or mud? Why did He breathe on people? Why did He permit healing to be transmitted by touching the hem of His garment? Why did He permit people to be healed by Peter's shadow, or by cloths and napkins that had been touched by Paul? Here we have objects which become instruments of God's power. The God who used the bones of Elisha to cause a dead man to come to life (2 Kings 13:21), used, and still uses, material things. It's not just "the Sacraments" that are sacramental. All of created realty is sacramental.
"Because it is not under the old covenant, they [physical things] do not CAUSE the spiritual reality."
I may have expressed myself inadequately ("No!" "Yes!") but I'm pretty sure I didn't say that physical things "cause" spiritual reality. That would be some kind of superstition. God uses physical things because of His gracious condescension to us, His accommodation to our natures. It is His will and pleasure to involve His creatures very, very often as secondary causes of things of which He is the primary cause.
In some cases, it might be like a dad who lets his little son help move the piano. The dad doesn't "need" the little boy to help; but he knows the little boy needs to help. And that pleases Him.
Of course God is interested in the physical and our body is important to Him. Jesus took a horrible beating to procure our healing. Isaiah 53:5 But he was pierced for our transgressions; he was crushed for our iniquities; upon him was the chastisement that brought us peace, and with his wounds (stripes) we are healed.
We are to glorify God in our bodies....1 Corinthians 6:20 Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body.
One thing I have noticed over the last decades is a decrease in the recognition of the spiritual. We are spiritual beings who operate in both the physical and spiritual realms simultaneously. Believers are seated with Christ in the heavenly places (Ephesians 2:6) What happens spiritually affects the physical world and what we do physically has ramifications in the spiritual realm. But since what is seen is temporal and what is unseen is eternal, the spiritual realm is where the reality really occurs.
The problem with the idea that physical actions produce spiritual realities is that it precludes having the right heart.
For example, if the action of baptism is what saves, if it causes spiritual reality to occur, then is must do so always, without regard for the condition of the heart of the person being baptized. It must work because it does inherently.
If someone then says that it's the heart attitude that must also be right, then the action of baptism is does not really save, does not really cause the spiritual reality to take place.
That is why God drove Adam and Eve from the garden. The Tree of Life gives life by eating of it. If Adam and Eve had eaten of that fruit, they would have lived forever in a state of sin, forever beyond redemption. It was an act of mercy on the part of God to keep them from eating of the Tree of Life.
That's the problem with declaring that a physical action produces a spiritual reality. If it doesn't affect the spiritual realm PERMANENTLY, then it doesn't do it at all.
I read something interesting recently about prayer and cannot remember where I read it, but it is based on a verse in Psalms 115:6 The heavens are the LORD's heavens, but the earth he has given to the children of man.
The gist of the writer's take on it is that this is why God tells us to pray for things, that He will not act on earth without prayer, man asking Him to. In that way, we can and do participate in what He is doing on this planet. It also puts a tremendous importance and emphasis on prayer.
I had never heard it put that way before, but thought it was an interesting viewpoint.