Cardinal Vincent Nichols held a press conference as he prepared to attend the Pope's Synod on the Family in Rome next month.
Currently, Church law prohibits anyone who has been married and divorced from taking communion, but there had been hopes the Synod would review that.
The Archbishop of Westminster thinks this is unlikely. He said: "I don't see for myself where the area of manoeuvre opens up without quite a radical rethink of one or the other.
"Therefore, I go to this synod really intent on listening to what people have to say.
"There is a need to grasp again, refresh and deepen the Church's understanding of marriage as a sacrament. It needs to come back to the fore.
"A marriage in the Catholic understanding – when it is embraced in the right intention, spirit and form – is an act of God. The husband and wife become ministers of God's grace to each other."
The Cardinal added that people could still take part in Mass even if they didn't take Communion, and that the Church had to be more understanding.
He said: "I believe Pope Francis is calling for a return to that 'lived sense' of the mercy and compassion of God, who always accompanies us. One of the challenges is to find ways to recreate a 'culture of mercy' in the Church.
"We also need to be clear that there is a distinction between that culture of mercy and the acts that are necessary for forgiveness and conversion. Mercy is the air we are to breathe; forgiveness and conversion are the pathway we are to walk."
The Synod on the Family takes place in Rome between 5th and 19th October.