The ability to have a pure heart comes from God, and he graciously gives us that ability.
Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord; seeing that His divine power has granted to us everything pertaining to life and godliness, through the true knowledge of Him who called us by His own glory and excellence. (2 Peter 1:2-3)
I bold faced "everything" to make a point. If we cannot have a pure heart, as some falsely claim, then God has not given us everything we need to be godly. Such a belief defies this passage. Since God has given all we need to be godly, then certainly we are capable.
And we are more than merely capable; we overwhelmingly conquer (Romans 8:37). The power of God's spirit destroyed the old self and gave us a new heart. We are new creatures. The old has passed away (2 Corinthians 5:17). Thanks be to God for His awesome provision for holiness!
This is probably my last post under this topic. I will likely come back to this subject later, but probably under a different heading.
I will finish by providing a link to a tremendous sermon by John Wesley that gives his views on Christian holiness. Click Here