Smoke covered the mountain that had been engulfed in cloud and bombarded with lightning moments before. On the peak flames rose above the smoke. As the people stood gazing upwards, the mountain itself began to shake violently. Suddenly, the trumpet sounded, beckoning them to the boundary at the foot of the Mount of God. They had been warned not to approach the mountain, and many wouldn’t get near it if their lives depended on it. However, some wanted to get closer. They wanted to see what Moses was seeing. They wanted to see God. The glory was so close. Maybe they could get close enough to get just a glimpse! But they had been warned: any who tried to break through to gaze at the LORD would surely die.
This account, found in Exodus 19, reminds us that we cannot see the glory of God. Even when he hides His splendor in a cloud or smoke, the earth can barely handle it. David, perhaps reflecting on this passage, asks in Psalm 24, “Who may ascend into the hill of the LORD? And who may stand in His holy place?” Who indeed?
Holiness means “set apart.” God is set apart from His creation in two ways. First, He is God and we are not. This will never change. Not now. Not in eternity. God will always be separate from His creation as entirely “other” than we are. However, another aspect will change. That is His distance from us in purity. He is pure, free from anything that would taint His character, and He will not allow anyone or anything into His presence that Has been sullied by sin. So, who can stand in God’s presence? Jesus paraphrases David’s response in Psalm 24 this way: “Blessed are the pure in heart, for they shall see God” (Matt. 5:8). One day, we’re promised, some will be able to enter His presence and withstand His holy purity, for they too will be pure.
We tend to think of purity in a sexual way, particularly for single people saving themselves for marriage. So we read a verse like Matthew 5:8 and think it must mean that if I’m not lusting after anyone, actively committing adultery, or addicted to pornography or salacious romance novels, I’m good. While I would agree that if you’re ensnared in sexual sin of any kind, you’re not pure in heart, I would also have to say that this sixth Beatitude means much more than that.
From the beginning God has desired one thing from His people: their whole hearts. The first and greatest command makes this clear: “You shall love the LORD your God with all your heart” (Deut. 6:5). It’s this command that Jesus expounds upon in His most famous sermon. Matthean scholar, Dr. Jonathan Pennington, says it this way: “Jesus’s consistent emphasis throughout [the Sermon on the Mount] is that whole-person righteousness (from the heart, in the inner person) is what real righteousness, godliness (godlikeness), and holiness look like.”  To put it another way, the whole point of the Sermon is that we love God with 100% of our hearts, or, that our hearts be pure.
The word pure means “free from every admixture of what is false.” I don’t know about you, but that does not describe my heart. My heart is better described by the prophet Jeremiah: “The heart is more deceitful than all else and is desperately sick; who can understand it?” (Jeremiah 17:9). I love God, but I also love my idols. I read my Bible and swear to worship only God; two minutes later, I check my phone, and suddenly my heart is chasing down a lover of its own. This is what we have to work with, yet Jesus is telling us that if we want to flourish, to live the “good life” that God intended and see God, we must be pure in heart. If that’s the case, I don’t stand a chance! Far from being pure and whole, my heart is splintered and looks more like a windshield that had a close encounter with a baseball than like silver refined by fire.
But I desire to be counted among the blessed and to see God, don’t you? I want to be pure in heart, but how do I get there? First, we glory in our union with Christ. Though Moses repeatedly told the Israelites as they were about to enter the Promised Land that God required their whole hearts, the rest of the Old Testament is a sad witness to their failure to keep that command. They courted idols, scorned the God of their salvation, and made half-hearted shows of worship generation after generation. Clearly, there had to be another way.
You know where I’m going with this. That better way came in the form of a Babe in a manger, the Man of Sorrows, the suffering Servant hanging naked on a cross. But here’s the glorious hope for our wicked, splintered, adulterous hearts: “For I am crucified with Christ; nevertheless, I live, yet not I but Christ who lives within me” (Gal. 2:20). My duplicitous heart was crucified with Christ that day, and His wholeness of heart was credited to my account (see also 2 Cor. 5:21).
That’s the glorious good news. And while every word of it is true, we still battle our fleshly hearts because though the power of sin has been broken in our lives, we still grapple with its presence. How do I become pure of heart while waiting for the Kingdom of God?
The answer takes us to a surprising and uncomfortable place: the furnace of adversity. Job, the quintessential sufferer, explains: “But He knows the way I take; [When] He has tried me, I shall come forth as gold” (Job 23:10). The Apostle Peter elaborates on this idea: In this [the Gospel] you greatly rejoice, even though now for a little while, if necessary, you have been distressed by various trials, so that the proof of your faith, being more precious than gold which is perishable, even though tested by fire, may be found to result in praise and glory and honor at the revelation of Jesus Christ. (1 Pet. 1:6-7). Simply put, we can, as James says, “Count it all joy” when we encounter trouble because God is at work uniting our hearts. He’s masterfully refining all that isn’t pure, stripping us of idols and independent spirits, so that what remains may be pure. Not all refining is in a blazing furnace. Sometimes it comes by way of a stay-at-home order or lost car keys or a flat tire. Our wise Father doesn’t waste a single circumstance in making us pure.
Of course, while He works, we work too. We must be killing the sin that adulterates our hearts, sometimes taking radical steps to draw near to God. Consider what pockets of sin you’d rather keep hidden from God. Where is your allegiance to a king other than the King of Kings? We’re called to put these things to death. And that’s hard, just like God’s purifying process. But we’re promised a reward that will outweigh it all. We’ll be able to stand on that mountain that is no longer veiled in smoke and behold the full glory of the Lord our God!
 The Sermon on the Mount and Human Flourishing, pg 82.
 Strongs, G2513, katharos