52 Supposing that the two free wives point to the New Testament, by which we are called to liberty, what is the meaning of there being two? Perhaps because in Scripture, as the attentive reader will find, we are said to have two lives in the body of Christ—one temporal, in which we suffer pain, and one eternal, in which we shall behold the blessedness of God. We see the one in the Lord's passion, and the other in His resurrection. The names of the women point to this meaning: It is said that Leah means Suffering, and Rachel the First Principle made visible, or the Word which makes the First Principle visible.
The action, then, of our mortal human life, in which we live by faith, doing many painful tasks without knowing what benefit may result from them to those in whom we are interested, is Leah, Jacob's first wife. And thus she is said to have had weak eyes. For the purposes of mortals are timid, and our plans uncertain. Again, the hope of the eternal contemplation of God, accompanied with a sure and delightful perception of truth, is Rachel. And on this account she is described as fair and well-formed.
This is the beloved of every pious student, and for this he serves the grace of God, by which our sins, though like scarlet, are made white as snow. For Laban means making white; and we read that Jacob served Laban for Rachel. No man turns to serve righteousness, in subjection to the grace of forgiveness, but that he may live in peace in the Word which makes visible the First Principle, or God; that is, he serves for Rachel, not for Leah. For what a man loves in the works of righteousness is not the toil of doing and suffering.
No one desires this life for its own sake; as Jacob desired not Leah, who yet was brought to him, and became his wife, and the mother of children. Though she could not be loved of herself, the Lord made her be borne with as a step to Rachel; and then she came to be approved of on account of her children. Thus every useful servant of God, brought into His grace by which his sins are made white, has in his mind, and heart, and affection, when he thus turns to God, nothing but the knowledge of wisdom.
This we often expect to attain as a reward for practising the seven precepts of the law which concern the love of our neighbor, that we injure no one: namely, Honor your father and mother; You shall not commit adultery; You shall not kill; You shall not steal; You shall not bear false witness; You shall not desire your neighbor's wife; You shall not covet your neighbor's property. When a man has obeyed these to the best of his ability, and, instead of the bright joys of truth which he desired and hoped for, finds in the darkness of the manifold trials of this world that he is bound to painful endurance, or has embraced Leah instead of Rachel, if there is perseverance in his love, he bears with the one in order to attain the other; and as if it were said to him, Serve seven other years for Rachel, he hears seven new commands—to be poor in spirit, to be meek, to be a mourner, to hunger and thirst after righteousness, to be merciful, pure, and a peacemaker. A man would desire, if it were possible, to obtain at once the joys of lovely and perfect wisdom, without the endurance of toil in action and suffering; but this is impossible in mortal life. This seems to be meant, when it is said to Jacob: "It is not the custom in our country to marry the younger before the elder." The elder may very well mean the first in order of time. So, in the discipline of man, the toil of doing the work of righteousness precedes the delight of understanding the truth.
Source: Reply to Faustus the Manichaean (New Advent)