"So teach us to number our days, That we may gain a heart of wisdom."
In order for a man to know how to live his life, he must first understand that his time on the earth is short. Knowing that man's life is only a vapor (Psalm 39), he will be motivated by the grace of God to live his life in a manner that pleases the Lord. The Psalmist asks God to "teach us," implying that a heart of wisdom comes from the Lord and is not inherent in man. It must be pursued and regarded as more valuable than gold and silver (Proverbs 3:15).
Often, Christians believe they know what is best for their own lives. It can be easy to neglect the calling of the Lord in favor of selfiesh, fleshly desires which seem wise, but in the end lead to death (Proverbs 14:12 ; 16:25). Instead, the Christian must renounce his own understanding (Proverbs 3:5) and ask that the Lord teach him and give him a heart of wisdom. In doing so, he will preserve his life, for anyone who loses his life for the sake of Christ will actually gain it (Matthew 10:39).