In Finland, the most important Church (and national) holidays are Christmas (Dec 25), Easter, and Pentecost.
Other important national holidays connected to the Lutheran Church year (and celebrated with a Mass) are the first Advent Sunday (we light one candle, one more candle is added every coming Advent Sunday, "Favourite Christmas Carols" sing-along events), Christmas Eve (trad. Christmas dinner & presents; all shops et al close/stop at noon, schools are on break between Christmas and New Year/Epiphany) and Boxing Day, New Year's Day (celebrated with a Mass), Epiphany, Holy Week (evening services, concerts, passions), Maundy Thursday, Good Friday (no Mass, a solemn Service of the Word), Holy Saturday, Easter Monday, Ascension Day, Saint John's/Midsummer, Michaelmas (trad. pecial children's/family services), All Saints' Day (visiting the graves and lighting candles).