St. Seraphim of Sarov on the Fasts

Once there came to him a mother who was concerned about how she might arrange the best possible marriage for her young daughter. When she came to Saint Seraphim for advice, he said to her: “Before all else, ensure that he, whom your daughter chooses as her companion for life, keeps the fasts. If he does not, then he is not a Christian, whatever he may consider himself to be.” (From a sermon of Metropolitan Philaret, quoted in The Ladder of Divine Ascent, pub. Holy Trinity Monastery, Pg. xxxiii.)

Source: http://www.abbamoses.com/fasting.html