[Psalm 53] is almost identical to Psalm 14, and the two psalms were probably alternate versions of the same hymn before they were included in the Psalter. The two hymns serve the same function, namely, to mourn the fact that mankind does not seek after God and thus treats God's people cruelly.
-- Source: ESV Study Bible (http://www.esvstudybible.org/search?q=psalm+14%2C+53)
