Cardinal Sean Brady has urged people opposed to abortion to make their views known in a reasonable and forthright manner.
As the Government finalises legislation and regulation to allow for a pregnancy to be terminated if the mother's life is in danger, the Catholic primate said it would be a defining moment for Ireland.
"Public representatives will be asked to decide whether a caring and compassionate society is defined by providing the best possible care and protection to a woman struggling to cope with an unwanted pregnancy or by the deliberate destruction of another human life," he said.
"I hope that everyone who believes that the right to life is fundamental will make their voice heard in a reasonable, but forthright, way to their representatives, reminding them that the right to life is conferred on human beings not by the powerful ones of this world but by the Creator.
"There is no more important value than upholding the right to life in all circumstances."
The Cardinal also used his message to urge more action to alleviate the conditions of the least well-off in society.
"I believe this failure to prioritise the elimination of child and family poverty in the reform of the tax and welfare system, in any jurisdiction, is unworthy of a society which claims to have a paramount concern for children," he said.
Cardinal Brady also talked about the pressure and anxiety people face.
He said he wished to see faith and public life move beyond what he called "the sometimes negative, exaggerated caricatures of the past".
And the cleric warned that neither politics alone, nor economics, can address our need for meaning and purpose in life.
"Unprecedented financial pressures, and an ever-increasingly aggressive public culture, along with social, moral and spiritual fragmentation, are leading to lives being overwhelmed by stress, intolerable interior isolation and even quiet despair," he said.
"We can, and should, do better than this in striving to create a society truly worthy of the dignity of the human person.
"It would have to be a society in which the emotional, moral and religious as well as the economic needs are met. The consequences of failing to cater for those needs can be tragic."