When angels appear in Scripture, they almost always preface their message with the words, "Do not be afraid!" As humans, we don't like to do or see things out of the ordinary. While it's true that some people are more adventurous than others, there's a point in which something becomes so unexpected that anyone would recoil in fear.
If a spaceship full of martians landed tomorrow, everyone would be freaking out. No one in their right minds would walk up to the new arrivals, shake their hands (if they had any), and give them a warm welcome. Instead, a few, carefully selected, heavily trained people would make an extremely cautious approach. Why? Because that's how people react when they face the unknown— they're terrified.
Angels, however, aren't just different— they're glorious. In this present age they are, as far as we know, the closest beings to God. The angel Gabriel, after identifying himself, told Zechariah, "I stand in the presence of God" (Luke 1:19). Angels reflect God's holiness and justice. It is the overwhelming purity of angels in combination with their differences from the natural realm that makes them so fearsome.
Consider this then: if angels are so fearsome that they must say "Do not be afraid," what is Christ like in all His glory? What is it like to see Christ unveiled, seated at the right hand of the Father?
Jesus Christ must be the most fearsome of sights. Daniel fell down at the sight of Christ (Daniel 8:18), so did the apostle John (Revelation 1:17). If it were not for Christ's own righteousness that clothes us and makes us pure, how much more terrifying would the sight of Him be! Let us always be aware of Christ's fearsome glory, always looking to Him in eager, awed anticipation. For one day, we will be with Him. One day, we will be like Him, and we will reign with Him forever and ever!