The congress, the first of its kind in Lithuania's history, will take place from Friday through Sunday.
"We hope that these three days will bring together 10,000 people," Grusas told reporters on Thursday.
He said that the idea of mercy, which Pope Francis has made a key element of his pontificate, should permeate Lithuania as well.
Vatican State Secretary Pietro Parolin, the most senior cardinal in the Vatican hierarchy, is expected to come to Vilnius this week to participate in the National Congress of Mercy.
The congress is the biggest event of the Jubilee Year of Mercy in Lithuania.
