The grain that has fallen to the ground produces much fruit (Jn 12:24)
Our Lord compared himself to a mustard seed, for although he was the God of glory and eternal majesty he became completely small in that he willed to be born of a virgin in the body of a child. Thus he was placed in the earth when his body was laid in the tomb but, when he had risen from the dead through his glorious resurrection, he grew great on earth until he became a tree in whose branches nest the birds of the air.
This tree stands for the Church, which Christ's death has raised up in glory. As for its branches, these must be understood as the apostles since, just as branches are the tree's natural adornment, so the apostles are the adornment of Christ's Church through the beauty of grace they have received. And on these branches, as we know, dwell the birds of the air. Allegorically speaking, the birds of the air designate ourselves who, coming to Christ's Church, perch on the teaching of the apostles like birds on the branch.