Mt 5:8 Blessed are the pure in heart, for they will see God.
A pure heart is an undivided soul towards God. It is not so much that like ivory soap you’re 99.9% pure in the sense that you never do wrong or bad things. Although that is an effect of having a pure heart. For John says:
1Jn 3:8 [But] he who commits sin [who practices evildoing] is of the devil [takes his character from the evil one], for the devil has sinned (violated the divine law) from the beginning. The reason the Son of God was made manifest (visible) was to undo (destroy, loosen, and dissolve) the works the devil [has done].
1Jn 3:9 No one born (begotten) of God [deliberately, knowingly, and habitually] practices sin, for God’s nature abides in him [His principle of life, the divine sperm, remains permanently within him]; and he cannot practice sinning because he is born (begotten) of God.
1Jn 3:10 By this it is made clear who take their nature from God and are His children and who take their nature from the devil and are his children: no one who does not practice righteousness [who does not conform to God’s will in purpose, thought, and action] is of God; neither is anyone who does not love his brother (his fellow believer in Christ).
What it does mean is that your heart/soul/mind is undivided when it comes to spiritual union and desiring to do the will of God. There is nothing in you that prefers to do your will over doing God’s. For example: I want to go to church this Sunday, but football is on every Sunday. Or, God is asking me to help at a soup kitchen every Friday night and my friends just won’t understand why I am not hanging with them. Or, I can’t quit college and go on a missionary trip that God is calling me to, because my parents will simply not understand. To have a pure heart means to, in many cases in fear and trembling, do how God through your conscience is leading without letting your fears (desire to control), reasoning, or intellect over ride what God is prompting you to do.
You may think: How do I know if it is really from God, because it doesn’t make sense? Jesus said:
Jn 7:17 If any man desires to do His will (God’s pleasure), he will know (have the needed illumination to recognize, and can tell for himself) whether the teaching is from God or whether I am speaking from Myself and of My own accord and on My own authority.
Jn 7:18 He who speaks on his own authority seeks to win honor for himself. [He whose teaching originates with himself seeks his own glory.] But He Who seeks the glory and is eager for the honor of Him Who sent Him, He is true; and there is no unrighteousness or falsehood or deception in Him.
What this means is that if you have a pure heart in that you desire above your own will to do the will of God, then what seems right to do will be God’s will. But if one possess a divided heart he will doubt what is from God. However, if one, even though being a Christian, and in ministry if he desires to do his own will, what seems right to this person will almost without exception not be God’s will, but his own in his own estimation. This person has shown himself to not have a truly repentative heart. Listen how the Amplified Bible defines the word repent:
Ac 2:38 And Peter answered them, Repent(change your views and purpose to accept the will of God in your inner selves instead of rejecting it) and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of and release from your sins; and you shall receive the gift of the Holy Spirit
This is the reason why Jesus says: this is eternal life, to know God.
And also to those who did not feed Him or give Him drink who He was in spiritual union with: get away from me evil doers for I never knew you. Although they may have been in ministry, and did work for the Christian cause, even healing and deliverance, they never changed their perception of life in a manner which allowed the will of God into their hearts—allowing themselves to be in spiritual union with Jesus’ Spirit. Sadly this means they are still technically in rebellion to God’s will in their hearts. And what seems right to that person is his own self-righteousness—his own sense of right and wrong. Jesus was never in spiritual union with this person. They are not one with Him. And this is the measuring stick God will use to know if they love God and His will. Do they know Him? Do they recognize those who are in spiritual union with Jesus?