Archbishop Diarmuid Martin said the Church can no longer "simply presume that the faith will automatically be passed from one generation to the next or be lived to the full by its own members".
He said there was a need for adult faith formation which addresses adult questions about religion.
The WIN-Gallup International Religiosity and Atheism Index found that out of 1,000 polled just 47 per cent of Irish described themselves as religious.
This was down from 69 per cent in 2005.