The expression “pure in heart” refers to a person whose inner most thoughts, motivation and purpose are pure, clean, wholesome and good; this is the one who will see God. To see God is to believe in God, and even more basic, they believe God; such a person is blessed indeed.
The person who is not pure in heart will not see God, possibly because he would rather not see Him. The person who is not pure in heart is one whose inner motivations are not wholesome or good, but are more likely centered on self, gain and getting what they want at whatever cost; they are not blessed because there is little room in their lives for a relationship with Him.
Life Project Blog 
This is good. So many times I find that what we call the prescriptive commands of God in His Word are very much the descriptive results of our choices regarding Him. I think you are right about this. We usually see, “Be righteous and holy, or you won’t get to see God.” What you have laid out is, “If you are unrighteous and unholy, there’s no way you’ll be able to see God anyway…even if He was right in front of you.”
The longer I live, however, the more I see that God – even in all His glory, holiness, righteousness and power – desires, longs for us to know Him and be near Him and have relationship with Him. If we are unwilling, continuing in our pride and rebellion – our self-centeredness – there is no way this can happen. When I humble myself, that’s when I can receive the gift of His presence. The gift is actually Him.
You’ve given me a lot to think about today. Thank you.
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The one who won’t see God is the one who has placed something or someone (themselves perhaps) in the place that is rightfully God’s. Repentance and turning to God is the only answer for them if they want to see God! Blessings to you today.