John Chrysostom — as excerpted in the Catena Aurea on Matthew 13:44

“The foregoing parables of the leaven, and the grain of mustard-seed, are referred to the power of the Gospel preaching, which has subdued the whole world; in order to shew its value and splendour, He now puts forth parables concerning a pearl and a treasure, saying, The kingdom of heaven is like unto treasure hid in a field. For the Gospel preaching is hidden in this world; and if you do not sell your all you will not purchase it; and this you ought to do with joy; wherefore it follows, which when a man hath found, he hideth it.”