To unite as husband and wife. First of all, everything is analogical. Father gives the fundamental Principle pattern, centering on God. In love, vertical becomes horizontal and horizontal becomes vertical. God is vertical, becomes horizontal.
Man is vertical, becomes horizontal.
The love is horizontal, become vertical. In most propulsion processes there is a rotation of dimensions. In a hurricane of tornado, horizontal centripetal suction creates motion at right angles. This tendency of planar motion to become spherical is documented in Divine Principle. This is what is happening in America.