In Joshua 22 we read about the tribes of Reuben, Gad and Manasseh building an altar of witness, a permanent object to remind them and their descendants that they were part of the covenant made with God, to serve God and keep the law. They describe the altar as “a witness between us that the Lord is God.”
God says in Isaiah 28 “I am the one who has laid as a foundation in Zion, a stone, a tested stone, a precious cornerstone, of a sure foundation”.
Hebrews 11 describes faith as “the assurance of things hoped for, the conviction of things not seen.” We’ve never physically seen that sure foundation that God created. We have no physical monument to remind us of the covenant we’ve made with God. But through faith, we know that the sure foundation of Christ exists, that we can build our lives on the certainty of God’s promise. Through faith, we can be witnesses to each other, to encourage and remind of that covenant made with God, and help each other grow and develop in God’s love.