Wedding vows are not a declaration of present love but a mutually binding promise of future love. A wedding should not be primarily a celebration of how loving you feel now—that can be safely assumed. Rather, in a wedding you stand up before God, your family, and all the main institutions of society, and you promise to be loving, faithful, and true to the other person in the future, regardless of undulating internal feelings or external circumstances.
~~Tim Keller, "The Meaning of Marriage"
The “soul of marriage” is a mystery. The apostle Paul wrote: ‘“ Therefore a man shall leave his father and mother and hold fast to his wife, and the two shall become one flesh.” This mystery is profound, and I am saying that it refers to Christ and the church.’
Satan, and the world as his helper, is striking at the soul of marriage - in (at least) a two-pronged offensive.
Both of these are an attempt to strike at the very image of God. If we have a warped view of marriage, we will also have a warped view of God.
If we have a warped view of God, we will end up making Him in our own image...which is no god at all.
The first way I see involves striking at the image of Christ and His bride.
The second way I see involves striking at the image of God in creation.
One aspect of the "soul of marriage" is reflection of Christ and His bride. The beautiful wedding dance of headship and submission shows Christians what their marriages should look like, and Christian marriages should show the world what Christ and His bride look like.
Egalitarianism teaches that there are no gender roles in marriage - since Scripture tells us that Christian marriages reflect Christ and His bride, no gender roles in marriage = no leadership, stewardship, or headship of Christ over His bride.
This assault on the soul of marriage leads to a warped view of Jesus.
The second front of the battle is "4SR" (State Sanctioned Same Sex Relationships.)
The onslaught of the world against marriage, to force the recognition 4SR as "marriage," is stunning in its swiftness. Even five years ago, we would not be having this conversation.
While I fully believe that God the Father is beyond gender (is a spirit,) He DOES get to pick what gender He wishes to be recognized as. God chose "Father" - so that's what we know Him by.
That said, since He is beyond gender, the Bible makes sense:
So God created man in his own image,
in the image of God he created him;
male and female he created them.
It seems that God - in His own image, created male and female. Together, they form a "oneness" that reflects the image of God.
There is more, and I want to expand, but in a nutshell, these two points are the main offensives, with various strategies within those offenses, where Satan is attacking the institution of marriage.