How can I ever live up to what Scripture requires of me? "Be holy as I am holy" or "Therefore be perfect as your heavenly Father is perfect."
Let's look at the original meaning of the Greek, which is key to understanding what we are being told to do. In the first verse, 1 Peter 1:16, the word translated as "holy," is defined in the lexicon as dedicated, consecrated, to the service of God. It conveys the idea of being set apart for a special purpose. God told His chosen people His Law had this intent: "You are therefore to make a distinction between the clean animal and the unclean...thus you are to be holy to Me, for I the Lord am holy, and I have set you apart from the peoples to be Mine." (Leviticus 20:24-26) By following the rules God set out, the Israelites would stand out from all the nations around them as God's own.
The second verse you quoted, Matthew 15:48, tells us to "be perfect." The Greek word, translated as perfect, is defined in the lexicon as fully developed, complete, wanting nothing necessary for completeness. We are told in Philippians that God is at work in us to perfect the good work He began until the day of Jesus Christ. So attaining perfection is an ongoing process-one that will not be finished until the Lord returns.
It seems both verses are giving a direction to look when deciding on a standard of holiness or completeness for ourselves. Our natural instinct is to compare ourselves with our peers around us, where someone worse off than we are can be easily found. Yet that is not the standard God wants us to aim at. He wants our standards to be determined by His example.
While both holiness and perfection are a progressive work in our lives, in one sense they have already been accomplished. "For you are a chosen race, a royal priesthood, a holy nation, a people for God's own possession, so that you may proclaim the excellencies of Him who has called you out of darkness into His marvelous light." (1 Peter 2:9) We have already been made holy and perfect through Jesus Christ.
So relax: in God's eyes, you already possess the holiness and perfection of Jesus Christ. But He loves you too much to allow the rest of you to remain unchanged. What was given to us at the moment of our salvation is now being worked out in the outer man as well. He wants the very best for you, so He is at work to change you to match what has already been accomplished in your soul.
But even in your darkest days, when you see so clearly how much change is still needed, know it is not a matter of trying hard enough. When loving God and serving Him becomes all about obligation, our efforts quickly become legalistic and even self-serving.
So how do we pursue holiness without it becoming all about us? Jesus gave the answer to the lukewarm church at Laodicea in Revelation 3:20: "Behold! I stand at the door and knock; if anyone hears my voice and opens the door, I will come in to him and will dine with him, and he with Me." The answer to needed change is in a more intimate relationship with Christ. As we learn more about Him, we fall more deeply in love with Him. Service will be a joyful response to His great love for us, not an added burden to check off the list. He came to set you free from obligation to the rules. Really what He wants is your heart.