"The fact of the presence of the Holy One among us is the basis of three practical principles.
"First, 'Be holy, for I am holy'. At one level, our holiness is the condition of His presence. Our unholiness repels Him. But the reasoning is probably deeper than that. To be unholy is to run the risk of causing His wrath to burn - not now from the comparative remoteness of Mt. Sinai, but from within ourselves. His anger will burn in His temple - 'which temple you are' (1 Cor. 3:16ff). But why will His anger burn so fiercely against His own people - more fiercely against them than against 'the rest'? Because their unholiness compromises Him. He is their God. They bear His name. They must therefor hallow it; and when they do not, He is jealous for the sake of His name.
"Secondly, the vision of God's holiness is the basis of Christian service. We usually find the basis of our evangelism in the perception of human need and this is not to be dismissed as altogether irrelevant. But it is not the main emphasis of Scripture. Time and again the Bible indicates that the true constraint to prophetic testimony is an overwhelming and abiding vision of the holiness of God. It was so in the case of Isaiah - he 'goes' because he has seen the Lord high and lifted up (Isaiah 6:1). Similarly, compliance with 'the great commission' springs from the vision of the Lord as the One who has all the authority in heaven and earth (Matt 28:18). In the same way, Paul preached Christ among the Gentiles because it had 'pleased God to reveal His Son in me' (Gal. 1:16) - a revelation of such overwhelming force that it had laid him prostrate and helpless on the Damascus Road.
"Finally, the holiness of God must regulate and inform our worship. We are approaching the august and majestic One. our approach cannot, therefore, be flipant or trivial. It must be tremulous and respectful, even in its moments of greatest boldness. We must come with pure hearts and sprinkled consciences (Heb. 10:22). Above all, we must realize that we approach only by invitation and that the important thing is not to come in a way that we find enjoyable or enterntaining, but to come int he spirit, attitude and posture that He commands. Our Father, indeed: but our heavenly Father."
from Behold Your God by Donald Macleod