To be "holy" means to be sacred or set apart. When God sent Moses with the above words for the nation of Israel, He was calling them to be set apart from the rest of the world; different from the other cultures and unique to Himself. If you read on, you will find that what follows for the remainder of the book of Exodus and the following book of Leviticus are specific guidelines that detail exactly how Israel will be, in a very literal sense, set apart as a nation. First, God gives them a quick summation of His Law, commonly called the 10 Commandments. This is followed by chapter after chapter full of details concerning the building, weaving, and making of the items of worship; consecration of the priests and the people; sacrifices for atonement; and numerous precise laws covering topics from clean and unclean foods to handling disease or dead things to appropriate responses in various social situations. The Nation was to be set apart indeed! They were distinguished among the cultures of the time by the very rigorousness of the Law."Now, therefore, if you will indeed obey My voice and keep My covenant, you shall be My treasured possession among all peoples, for all the earth is Mine; and you shall be to Me a kingdom of priests and a holy nation. . . " Exodus 19:5, 6a
It is a grave misfortune that so many in the Church today do not cling to this idea of holiness, of being set apart. Many outright reject it. It is even thought by some that the Old Testament has no bearing on the Christian of today. It is considered by some to be obsolete and no longer relevant because it is the old covenant. That is a blatant untruth. In the letter to the Roman church, Paul writes: "For whatever was written in former days was written for our instruction, that through endurance and through the encouragement of the Scriptures we might have hope," (Romans 15:4). Jesus, Himself, says, "You search the Scriptures because you think that in them you have eternal life; and it is they that bear witness about Me," (John 5:39). It must be understood that the Scriptures both Jesus and Paul refer are none other than those found in the Old Testament -- the documents known today as the New Testament simply did not exist when those words were spoken (though some of them may have been in existence when Paul spoke, they were not widely known by the Christian church at the time of his speaking). So the importance of understanding that old Covenant is seen in these two verses and can be seen in many others throughout the New Testament, especially as evidenced by the multitude of times it is quoted and alluded to by Christ, the apostles, and the early church fathers.
And so my soapbox speech for the significance of the Old Testament to the modern Believer has been duly articulated. But what, you may ask, has this to do with holiness? I'm glad you asked!
For one, the theme of being set apart that runs through Exodus and Leviticus (and beyond) is a picture of what it should look like to the Christian of today to be set apart through the sacrifice of Christ. The words of Paul in Romans 12:-2b again illustrate this: "I appeal to you therefore, brothers, by the mercies of God, to present your bodies as a living sacrifice, holy and acceptable to God, which is your spiritual worship. Do not be conformed to this world, but be transformed by the renewal of your mind. . ." or in Romans 6: "What shall we say then? Are we to continue in sin that grace may abound? By no means! How can we who died to sin still live in it?" So it is by death we are set apart--by dying to sin and taking off the old man being made a new creation in Christ. We are not the same, and we should not look the same. By putting our faith in Christ and allowing Him to have His way in us, we should now understand that we are holy to God and set apart for His purpose.
When God commanded the Israelites to be holy and set apart, I have no doubts that He was looking forward to the day when His Son would die so that all those who put their faith in Him would become a people set apart for Himself. I do not think that there is a great chasm between the God of the Old Testament and the God of the New--He is the same God, the unchanging Rock of our salvation; He is the Beginning and the End, and He has never wavered in His great purpose nor has He mellowed with age or in any way wavered or vacillated. Rather, everything in the Old Testament points to Christ, gives insight into the nature and character of God the Father, and is useful for teaching, reproof, correction, and training in righteousness for the believer today. It is as relevant as Romans, as practical as James. It is no coincidence that a letter written by Peter to the early Christian church contained an echo of the words of Yahweh to Moses: "But you are a chosen race, a royal priesthood, a holy nation, a people for His own possession, that you may proclaim the excellencies of Him who called you out of darkness into His marvelous light."