You yourselves are our letter, written on our hearts, recognized and read by everyone. It is clear that you are Christ’s letter, produced by us, not written with ink but with the Spirit of the living God — not on stone tablets but on tablets that are hearts of flesh. (2 Corinthians 3:2, 3 HCSB)
Paul, the author of 2 Corinthians, was having trouble with the people in the church at the city of Corinth. They were displeased with him. His answer was these two verses. The people were his letter of recommendation. Paul loved them, they were on his heart for everyone to read.
Not only that, but the Holy Spirit had written a letter on the people. Not on stone tablets like the 10 Commandments but on their tender, beating hearts. The Holy Spirit has done the same on our hearts. We are a letter from God to those around us that his love for them Is spelled out in our lives.
The tablets of the 10 Commandments were hidden in the ark of the covenant, a golden box with golden angels on top. They were a very important part of Israel's beliefs. There were also a jar of manna and an almond branch in the ark. When Moses would meet with God His glory was on top of this box between the two angels. Inside was God's words carved on stone. Now, though, in these days, he meets each of us in our tender, beating hearts and writes His love there. And the place He used to meet Moses at the ark was in the Tabernacle in the innermost place. God met Moses in the heart of hearts of the Tabernacle. Now God meets us in His heart of hearts and we are His letters of recommendation.
The video attached shows a letter from the heart of one friend to one who is in some trouble. The letter is especially loving.