Leviticus 19 is part of the Holiness Legislation. The Lord YHWH tells Israel what they should and should not do in response to His covenant promise to love them and be their God. This is literally the faith response to grace. The Jewish Study Bible (252, 253) says that faithful obedience allows Israel to “absorb the effusion of divine Presence in their midst.” Absorbing the presence of God is a wonderful metaphor to describe God's unity with His people and is similar to 'theosis' in Christian faith. As Christians, we know that Jesus is the Divine Presence of God, and our "absorption" of His life is what Paul refers to in saying, Jesus is the Foundation and we are the Temple full of the Holy Spirit. It is noteworthy that when he says "you are" it is plural. Individuals are not the temple, the church is the temple The church is to be rooted in Him in obedient love which fills us with His Divine Presence--the Holy Spirit--which makes us holy.
The word holy has two different meanings as applied to God and other things. God is holy, which means He is infinitely transcendent and totally "other" to all we know. He alone is holy in Himself. A person becomes holy by being set apart or dedicated to God; literally to become His possession. God makes people, places and things holy by consecrating them to Himself. Therefore, the (Lev 19:1) command “you shall be holy for I am holy” can be paraphrased, “you shall belong to Me, because only I am above all else and worthy of you.” To be dedicated to God, however, is always about love and service.
Be clear; loving obedience to God is salvific. Being equally clear, our works do not and cannot 'earn' salvation. But salvation is not a ticket to enter a place called heaven. Salvation is rescue from sin and death, rescue from the devil, the fallen world, and from our own selves. Above all else, salvation is a loving relationship with God and His creation. We are born into the world separated from God. God alone can bridge that gap, but our loving, trusting obedience opens us to the Divine Life. The commandments order our relationship with the Law Giver. As Gentiles, we are not under the Jewish Law, but in Christ we are still called to obey and “absorb” God through love. There is much in the Torah which we can distance ourselves from, but there are other commands which are pressing concerns even for Gentiles!
Much of reading from Leviticus 19 is about justice. Israel's relationship with God is communal. The Lord puts limits on private property--“Do not harvest all your crops, leave some for the poor”—but He expects the poor to pick it themselves! He says that it is wrong to take advantage of the poor or the disabled, yet rejects partiality to the poor (or rich). Anger, hatred and vengeance are ruled out, instead Israel is to love. Jesus quotes this as the summary commandment: Love your neighbor as yourself. Love all, even the enemy! Love is an Old Testament command and at the center of the relationship Israel has with God.
"Absorbing God" by obedient love is a daily challenge. Discipleship is the faith response to Jesus. He is Savior but also Teacher. Jesus says that we defeat evil through non-violent love. If the Roman soldier demands you carry things one mile, then walk two. Your love is stronger than his oppression. If someone insults you with a back hand slap, you offer them the other cheek, asserting your humanity even as you suffer. They hate the enemy? You love and pray for him. Love the enemy and pray for the persecutor because they are children of God and you are a child of God. Just like Jesus. This is the perfection Jesus calls us to. The perfection* of love, God's love in us and through us. Love on a cross which forgives every sin. The love which saves he world. This is the life of God which we absorb in our journey to holiness. In today's often hostile and conflict riddled world it is a stunning reminder that our love and prayers for those we feel the worst toward are God's call. It is an amazing thing to ponder, but love from the Cross is exactly that.
[The word perfect* can be worrisome to many Christians. It seems to imply that we must be as perfect as God, understood in a moral sense. Obviously, it is beyond us to achieve such perfection. So are we doomed to hell? Once again, it is important to remember that Jesus says "you all (plural)" so this is a command for the group. Think of it as a team commandment, not as an individualized performance.
It is helpful to look at Matthew’s use of the term “perfect,” and in doing so we learn that his is the only Gospel where the word appears! It shows up twice, here and in 19:21. In the latter case Jesus tells a rich young man who has faithfully kept the commandments: “if you would be perfect, go, sell what you possess and give to the poor, and you will have treasure in heaven; and come, follow me.” Perfection means completeness. It means finishing the job. Jesus is telling the rich man that his love of wealth and possessions were still in the way (in spite of his keeping the Torah). Perfection in our reading today seems to be used in a similar way. Love is not limited to the ones to whom we are connected; but also those who oppose us. Kinship circles are broken open to include everyone in the family. To reach the fullness of Jewish faithfulness (remember He is talking to Jews) and by extension the fullness of Christian faithfulness--this is "perfection"--they/we must love as God loves.
It is also helpful to see how the Greek word is used in translations of the Hebrew Bible. Matthew read the Septuagint, and a brief look at Deuteronomy 18:13 (“you shall be blameless before the Lord”) can be helpful
Septuagint: teleios ese enantion kurion tou theou sou
Hebrew: tamiym ‘im YHWH ‘elohim
Hebrew "Tamiym": complete, whole, entire, sound, innocent, having integrity, healthy; without spot or blemish, perfect, upright
Greek "teleios": brought to its end, finished, wanting nothing necessary to completeness, perfect (of men-full grown, adult, mature)
In conclusion, to “be perfect” is not to be on a higher level of Christianity. It is also not the moral perfection of God. It doesn’t mean we never make a mistake or error. To be perfect is to love—to seek the good and salvation of—all people. It is to follow Jesus and allow Him to shape our mind and heart, body and soul. It is to open to the Holy Spirit and be God’s Temple. It is a gift but it is the fruit of hard work, disciplined effort and obedience. And it takes a lifetime and then some to accomplish!]