The Lord be with you
I have included many quotes drawn from Valerius Herberger’s The Great Works of God, recently published by Concordia Publishing House in two volumes. There is a chapter short enough to post in full. It is the first chapter in the second volume in the CPH books, and the first chapter in Part 3 of Herberger’s work. He is considering the time when Abraham and Sarah departed from the full promise of God and took matters into their own hands.
I. JESUS
So Constantly Occupies the Thoughts of Abraham and Sarah That in Their Sincere Longing for Him They End Up in Folly (Gen. 16:2)
Whoever would contemplate Genesis 16 to his own profit and good must do so with a pure, modest, chaste, and demure heart. When Sarah was seventy-five years old, she urged Abraham, then eighty-five years old, to marry her maidservant Hagar. Here we have a prime example of human reason. Whenever God tarries in His helping, we suddenly think ourselves capable of solving the problem and finding the answer. But He regularly 
makes a fool of our presumptions. Therefore “wait for the LORD; be of good cheer, and do not despair, and wait for the LORD” (Ps. 27:14). When God makes us a promise, He is sure to keep it, even if, as sometimes happens, it does not immediately come to fruition.
Abraham was persuaded by Sarah’s shrewd words. Behold, the godly often deceive each other with vain ideas. However, God in His exceptional wisdom allowed this to happen, for Abraham was to beget two rival peoples—a mystery that St. Paul explains in Galatians 4:22-31.
Ishmael is a type of all the self-righteous who trust in their fleshly birth and good works and think to please God thereby. Isaac, on the other hand, is a type of all humble hearts who cling only to God’s gracious promise and believe that they will be saved only by God’s goodness and mercy.
Consider the hearts of Abraham and Sarah here. What could have led these two to such a foolish plan with their maidservant? The truth is, they were led to it by their heartfelt longing for the Savior and Redeemer of the world, Jesus Christ, whom they deeply desired to see. In the midst of their noblest piety Abraham and Sarah went astray. Oh Lord Jesus, help me to walk in fear, and with godly Job and wise David to practice godliness and devotion when I begin any idea, plan, or endeavor. Govern me by Your Spirit that I may not wander from You but always keep on the path that is straight and pleasing to You.
O Lord Jesus, just as Abraham and Sarah yearned for You, so my heart pines for You also. “As the deer pants for fresh water, so my soul pants for You.” Lord Christ (Ps. 42:1). You never leave my heart for a moment. You fill my thoughts day and night. O my Lord Jesus, I long for You a thousand times a day. I have desired to depart and be with You (Phil. 1:21). Oh, come, Lord Jesus, yea, come soon (Rev. 22:20), that I may live and abide with You forever. Amen.
Herberger, Valerius The Great Works of God: Parts Three and Four: The Mysteries of Christ in the Book of Genesis, Chapters 16-50, 15-16