Here’s two wonderful poems with the same title. The first I’d always heard, but the latter I discovered recently and actually prefer. 

Marriage Takes Three by Perry Tanksley

I once thought marriage took

Just two to make a go,

But now I am convinced

It takes the Lord also.

And not one marriage fails

Where Christ is asked to enter,

As lovers come together

With Jesus at the center.

But marriage seldom thrives,

And homes are incomplete,

Till He is welcomed there

To help avoid defeat.

In homes where Christ is first,

It’s obvious to see,

Those unions really work,

For marriage still takes three.

Marriage Takes Three (Author Unknown)

It’s not enough just two you see, to complete His plan there must be three. 

As Husband and Wife you complete your love, with sacred vows and the Lord above. 

If together you’ll both kneel and pray, with sincere hearts as you end each day, 

And in all you do, if you put Him first, He’ll meet your needs and quench your thirst. 

It’s not enough, just two you see… to complete His plan, it takes all three