Psalm 14 and Psalm 53 are very close to being identical. The scholarly type that like to analyze and compare tell us the Psalms are not necessarily in chronological order and Psalm 54 was perhaps written before Psalm 14.
Back in college days in a Bible study class, I had an instructor that said something like, "When you see verses repeated in Scripture, it's a sure sign there is double importance to the meaning of those verses."
With that being said, let's see if there is an important message to these repeated Psalms. Read verse 1 in both of them......they say the same thing. "The fool hath said in his heart, there is no God."
Surface recognition of the verse would lead us to believe it is dealing with the atheistic person, which is only partly right. Looking closer, consider the words of the verse again. The psalmist's words say the fool is a person who says in his heart there is no God. Is there a possibility this could be speaking about a person who knows in his mind, there is a God, but convinces his heart there isn't a God? This would be a person who could easily justify his own actions, whatever they may be, by a heart that has convinced itself God doesn't exist. One writer says this is a person who really knows God, exists, but lives as though God doesn't exist.
Further, consider a Christian to be one who not only believes God exists, but also lives a life of surrender to the will of God. Then if the world could silence Christian influence through making God seem less real, the end result would be a people who believed in God while living like they wish he didn't exist. An example of this is seen in Saul who knew God existed, but wished there was no God, therefore allowing Saul to dispose of David without guilt.
Above everything we can learn from this, the importance of Christian influence becomes a priority of every child of God. The world continues to examine us and sees too many instances where we are a people professing belief in God but lives being lived like there is no God. Surely someone would call that foolish. Just like God's word is quick to warn us, "The fool says in his heart, there is no God."