First, the marriage of Adam and Eve was consecrated by God Himself. Marriage in fact is the first institution established by God for man. And it being the first must be important. So important that the Savior likens the relationship of Himself and the church as a marriage which will be consecrated in Heaven at the marriage feast.
As far as the importance here, because God established marriage, brought the woman to Adam for the express purpose of being his wife, even more than that, a vow or pronouncement was made by man that the woman will be flesh of his flesh and bone of his bone because she was taken out of man. In Genesis chapter two, the Bible says “And the Lord God caused a deep sleep to fall upon Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof; And the rib, which the Lord God had taken from man, made he a woman, and brought her unto the man. And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man.”
This same pronouncement is made over the bride and the groom by the man of God. Henceforth the last pronouncement made: “Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.” Now, just as it’s been for many a century, the bride and groom come to the man of God so that this pronouncement can be made to more witnesses. That’s why the pronouncement has to be made in front of witnesses.
One other thing that you need to look at. There is a pesky verse that gets in the way of many who don’t see the need to go in front of the man of God to be pronounced. In other words, shack up. The law says that unless a marriage has been solemnized, it will not recognize it as a binding marriage in their eyes. So, that pesky verse: “Put them in mind to be subject to principalities and powers, to obey magistrates, to be ready to every good work,” in Titus. So then, if a marriage hasn’t been solemnized, it is a double whammy. It isn’t recognized as a marriage by the church and also not recognized by the powers that be…
Marriage is a covenant made between a man and a woman before God. If it’s a covenant made before God, many would think twice about destroying the marriage that God has joined together by pronouncement of marriage. In my eyes it’s like breaking a promise to God to be faithful to the one He’s joined them together with. If there’s no covenant (pronouncement before witnesses) then God most certainly does not condone it. Matthew chapter nineteen says: “And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh? Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.”
Even one step further. Unless a marriage between a Christian and another Christian, or even a Christian and an unbeliever has been pronounced by the man of God or a magistrate in the sight of witnesses, before God, it is a unholy thing. The scripture says “For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband: else were your children unclean; but now are they holy.