Catena Aurea on Matthew 4:1–2: Augustine of Hippo

Otherwise; The sum of all wisdom is to be acquainted with the Creator and the creature. The Creator is the Trinity, Father, Son, and Holy Ghost; the creature is partly invisible, - as the soul to which we assign a threefold nature, (as in the command to love God with the whole heart, mind, and soul,) - partly visible as the body, which we divide into four elements; the hot, the cold, the liquid, the solid. The number ten then, which stands for the whole law of life, taken four times, that is, multiplied by that number which we assign for the body, because by the body the law is obeyed or disobeyed, makes the number forty. All the aliquot parts in this number, viz. 1, 2, 4, 5, 8, 10, 20, taken together make up the number 50. Hence the time of our sorrow and affliction is fixed at forty days; the state of blessed joy which shall be hereafter is figured in the quinquagesimal festival, i.e. the fifty days from Easter to Pentecost.