It is a daily call and response.

a)While all the beings in this world are created by God with a specific
pattern of behavior called natural law, the human beings are called
into existence personally by God. Life is, therefore, a call and response.
This is given at every moment and hence every moment ought to be a
response. In the case  of persons this call is specific to each one and
it manifest itself in different ways.In marriage it is the call of God given
to a man and woman mediated by each other. The life of the married
people will therefore be conditioned by each other. They respond to God
through their mutual love. They make their life meaningful by this mutual
daily response.

b)The human love becomes the sacrament of the love of God.They manifest
their response to God by their love for one another. By the sacrament of
matrimony each becomes a grace to the other. Their human conjugal love
becomes consecrated love. This will not  take place automatically.
Since they carry with them their belonging to sinful Adam and Eve, they
have to be constantly struggling to keep their love for one another free
from selfishness. It is asceticism of self-denial which makes their human
love become the symbol of divine love.