He speaks of a wonderful union of husband and wife.
How beautiful, then, the marriage of two Christians, two who are one in hope, one in desire, one in the way of life they follow, one in the religion they practice.
They are as brother and sister, both servants of the same Master. Nothing divides them, either in flesh or in Spirit. They are in very truth, two in one flesh; and where there is but one flesh there is also but one spirit.
They pray together, they worship together, they fast together; instructing one another, encouraging one another, strengthening one another.
Side by side they face difficulties and persecution, share their consolations. They have no secrets from one another, they never shun each other's company; they never bring sorrow to each other's hearts… Psalms and hymns they sing to one another.
Hearing and seeing this, Christ rejoices. To such as these He gives His peace. Where there are two together, there also He is present, and where He is, there evil is not.
Unfortunately, Tertullian later fell into the heresy of Montanism, and his views became somewhat rigorous. He opposed a second marriage after the death of a spouse, and he even eventually didn't favor marriage at all.
But in his earlier Catholic writing, as seen above, he penned some beautiful words for Christian spouses.