Who may ascend into the hill of the Lord?
And who may stand in His holy place?
He who has clean hands and a pure heart...
Webster defines the word "pure" as being unmixed with any other matter. Watchman Nee uses the word "single-hearted". Perhaps the Psalmist captures the essence of being pure of heart in these words: "Besides Thee, I desire nothing on earth."
The one who is pure in heart has no desire on earth but God. He will sell everything to buy the field with the treasure. He will purchase the pearl of great price. He has no other goal in life than to serve God. He is the faithful servant whom the Master finds doing His work when He returns.
This one has pure motives. He neither hides nor harbors secret desires that are opposed to God or His kingdom. He seeks the kingdom of God and His righteousness. He does not straddle the fence between earth and heaven waiting to see which holds the greatest advantage or promise for him. The man of purity chooses his side before the outcome is known and he risks everything he has on earth. He serves God with no thought of reward. In fact, He would serve God if there were no reward.
This one weeds out of his life every hindrance to godliness; he kills every wrong or adulterous desire; he makes captive every base or covetous thought. His heart is steadfast toward his God and he guards himself from any other affection. He hides God's word in his heart that he might not sin against Him. In other words -- the man who is pure in heart walks before God with all his heart.
Search me, O God, and know my heart today;
Try me, my Savior, hear my prayer, I pray.
See if there be, some wicked way in me.
Cleanse me from every sin and set me free.