The following is Luther's commentary on marriage as
  he considers Abraham telling Eliezer to find Isaac a wife from among his
  relatives in Genesis 24:1-4 ( Luther's Works Vol. 4, pages 226-228.)
  Luther has much more to say about marriage in the rest of the chapter but this
  an outstanding introduction on the subject delivered to his seminary students.
  Therefore it is not without purpose that I am so often stressing and
  warning in what way so important and so sacred a matter should be approached
  in order that the authority of parents and the reverence of children toward
  them may be preserved. A son or a daughter should seek advice from those who
  are both capable of giving advice and, because of the divine institution and
  blessing of God, are able to counsel. The parents, on the other hand, should
  not be unyielding and rude. They should not urge their children to contract
  marriage with those whom they do not love; nor should they rashly restrain
  them from loving decent people unless they have chosen persons who are not
  suited to them. Parents should keep in mind the natural affection and
  inclination which God has implanted and should put nothing in the way of
  honorable love.
  Thus when Samson's parents became aware that he loved a Philistine woman
  and he asked that she be given to him as his wife, they permitted him to marry
  her, even though she was a heathen (Judges 14:1-4).
  But I warn again that for entering into marriage it is above all necessary
  to call upon God that He may choose and bestow the wife or husband. If this is
  done, God's blessing and all good fortune in marriage follow. God gives the
  husband the grace to have patience and to take the weakness of his wife in
  good part, and that she, in turn, may be able to adjust herself to her
  husband's ways. On the other hand, where fear of God and prayer are not added,
  irritations very easily occur. From these originate hatred, quarrels, enmity,
  and perpetual dissension. I have often seen completely unhappy marriages of
  this kind, and they commonly happen to those who follow the pope and the
  canons.
  But where people enter into marriage in a lawful and saintly manner in
  accordance with the ordinance and institution of God and are sure about the
  will of God and of their parents, the greatest disagreements and dangers are
  often overcome without any trouble and difficulty with the help of God and
  with a good conscience, which is certain that if anything unfortunate occurs,
  it does not happen by chance but in accord with the good will of God, at whose
  bidding they have entered into this kind of life. The papists see none of
  these things; they do not take into consideration the material, the efficient,
  or the final cause of marriage but consider it to be the kind of copulation
  that takes place in fornication.
  In the Law of Moses clandestine betrothals were so sternly forbidden and
  condemned that parents were permitted to declare them null and void even
  though intercourse had taken place (Ex. 22:16-17). Although we neither can nor
  must follow that law-for the forensic matters and the decisions of the Mosaic
  Law are not binding for us-nevertheless it is a Law which was written and
  proclaimed by God and our opinion is given powerful support by its example and
  testimony. Furthermore, we have on our side the civil law, which the canonists
  and all subjects of this empire are equally bound to obey.
  When Moses states in the text that the Lord blessed Abraham in all things,
  he has in mind all the riches of marriage. They are called blessings. Whatever
  the head of the household possesses, all this Holy Scripture is in the habit
  of calling a blessing. If people knew and believed this, there would not be so
  much plundering and unlawful gain in the world. But the majority live without
  praying and therefore also without a blessing. And in this unconcern they
  enter into marriage; they seek and heap up wealth without the blessing about
  which they do not think even once during their life. How few peasants and
  burghers there are who have God's blessing and own their possessions without
  doing wrong to others! Everything is full of usury, greed, and covetousness.
  But if you want to enter into a marriage with God's blessing seek the
  Lord's counsel first of all, and pray: "Lord God, give me a wife and
  daily bread." God regards those prayers with favor and answers them.
  "I have made you man and woman," He says. "Why would I not
  support you? But refrain from the wrong of plunder and theft."
  Therefore where a man and a woman are joined by God and in accordance with
  God's definite will, there is a marriage; and spouses who know this very
  easily bear and overcome whatever adversities befall them. Thus it is the
  first and greatest blessing if you know that you have entered into marriage in
  accordance with God's will and that you have taken a wife because you were
  compelled by necessity, in order to avoid sin.
  Whatever God then bestows, to all those good things you should give their
  true name and say: "This son or daughter the Lord has given to me; this
  field, meadow, cow, and goat God has given to me, and it is a divine
  blessing."
  That is truly a very beautiful and very happy marriage in which there is
  inscribed both on the table and on the bed: "he favor, will, and good
  pleasure of God." These are true and boundless riches, but such blessings
  you will not find in the canons. Thus the patriarch Jacob says below (Gen.
  33:5): "These are the children whom God has given me," surely
  because of extraordinary favor and blessing. These people are aware of and
  know the Creator and His creature; they realize whence they originated and
  whence they receive everything.