St. Peter teaches that:

[A]s He who called you is holy, you also be holy in all your conduct, because it is written, “Be holy, for I am holy.” 1 Peter 1:15-16

So how does one be Holy? Is that just a platitude or is it actually achievable?

First of all, what is holiness? What does it mean to be holy?

At the outset, we should recognize that holiness, according to the scriptures, is an attribute of God. He is holy. Therefore, holiness is found in its fullness in Him.

In a biblical sense, it means to be set apart; to be sacred, to be worthy of veneration. In the scriptures, we see that places, things, and people can be holy, but in each of these cases, the holiness is found in its relation to God alone. Holy places, things, or people are sanctified or consecrated and thus are exclusively God’s. Finally, holy things, places, or people can lose their holiness by being defiled or relegated to common use.

We’re first introduced to the concept of holiness before the law was given to Moses.

The first mention in the Scripture of something being holy is in Exodus 3 in which Christ appears to Moses in the burning bush and tells him to remove his sandals because the ground upon which he stood is holy.

Remember that at man’s expulsion from Paradise Adam and Eve received from God garments of skin. These garments were for their protection; a buffer between them and the ground that was cursed because of their sin.

According to St. Ambrose of Milas, Moses was told to remove his sandals "so that when he was about to call the people to the kingdom of God he might first put aside the garments of the flesh and might walk with his spirit and the footstep of his mind naked."

Moses had to remove his sandals to approach God not because his sandals were dirty or sinful, but because it signified the removal of the garments of skin and the restoration of mankind through communion with Christ.

St. Paul teaches that "[H]e hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will…" Ephesians 1:4-5

To put it another way, God chose us in the Son before the creation of the world to become His adopted children through communion with the Son, who condescended to us by humbling Himself to the point of taking on human flesh in order to destroy death and redeem humanity by joining it to his divinity.

So that, according to St. Paul:  

[T]he God of our Lord Jesus Christ, the Father of glory, may give unto you the spirit of wisdom and revelation in the knowledge of him: The eyes of your understanding being enlightened; that ye may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints, And what is the exceeding greatness of his power to us who believe, according to the working of his mighty power, Which he wrought in Christ, when he raised him from the dead…” Ephesians 1:17-23 KJV

According to St. Leo the Great, Pope of Rome (A.D. 461):

He himself says, “Be holy, for I am holy,” that is to say, choose me and keep away from what displeases me. Do what I love; love what I do. If what I order seems difficult, come back to me who ordered it, so that from where the command was given help might be offered. I who furnished the desire will not refuse support. Fast from contradiction, abstain from opposition. Let me be your food and drink. None desire in vain what is mine, for those who stretch out toward me seek me because I first sought them.

And from a sermon of St. Philaret of Moscow, given on September 23, 1847 we learn:

“Every Christian should find for himself the imperative and incentive to become holy. If you live without struggle and without hope of becoming holy, then you are Christians only in name and not in essence. But without holiness, no one shall see the Lord, that is to say they will not attain eternal blessedness. It is a trustworthy saying that Jesus Christ came into the world to save sinners (I Tim. 1:15). But we deceive ourselves if we think that we are saved while remaining sinners. Christ saves those sinners by giving them the means to become saints.”

FInally, let me leave you this encouraging quote from St. Basil:

It is not he who begins well who is perfect. It is he who ends well who is approved in God's sight. ~ Saint Basil