As I've learned more about God and His work, it amazes me what depth there is to all that He does. One example of this is the sacraments. When we took them on Easter a few weeks back, I nearly wept it was so awesome.
As a Christian, we're continually called to live by faith, and not by sight (2 Corinthians 5:7), to trust in that which is unseen (Hebrews 11:1). Yet in spite of these commands, we're sinful and broken. We lack the faith to move mountains, the trust to look to that which is not seen or touched.
And God gives more grace (James 4:6a). He has given us physical signs and seals to point to the spiritual reality. He tells us that the wind blows where it wishes and we do not know where it comes and where it goes, so it is with those born of the Spirit (John 3:8), but then He gives us the sign of that very action in baptism! We're sprinkled clean spiritually (Hebrews 10:22), and given the physical sign and seal to point us to that act!
Similarly we cannot see Christ's body broken for us. I know He died, but did He die for me? The command is to believe it. But God gives us (me!) more grace in our (my!) weakness. God gives us the Lord's Supper, in which He proclaims "this is my body, given for you... This cup is the new covenant in my blood, which is poured out for you." (Luke 22:19-20)
I've never seen God cleanse a heart. I've never seen God break Jesus for sinners. He works in invisible ways and his footprints were not seen (Psalm 77:19). But God shows more grace for my weakness. He gives signs and seals to point me to the fact that yes, these things have happened and are true.