Ye Shall Therefore Be Perfect, As Your FATHER Who IS In The Heavens IS Perfect

Be ye therefore perfect. — Literally, Ye therefore shall be perfect–the ideal future that implies an imperative.
Your Father which is in heaven.–The better reading gives, your heavenly Father. The idea of perfection implied in the word here is that of the attainment of the end or ideal completeness of our being. In us that attainment implies growth, and the word is used (e.g., in 1Corinthians 2:6; Hebrews 5:14) of men of full age as contrasted with infants. In God the perfection is not something attained, but exists eternally, but we draw near to it and become partakers of the divine nature when we love as He loves:
——“Earthly power doth then show likest God’s
When mercy seasons justice.”

Pulpit Commentary
Verse 48. – In Luke 6:36, “Be ye merciful, even as your Father is merciful,” we have certainly a reminiscence of the same saying, and, almost as certainly, from the smoothing away of difficulties, a less original form of it. Be ye therefore perfect; Revised Version, ye therefore shall be perfect (ἔσεσθε οϋν ὑμεῖς τέλειοι). The form is based on Deuteronomy 18:13, τέλειος ἔσῃ. While the introduction of ὑμεῖς emphasizes the contrast between Christ’s disciples and those who followed the usual deduction from the Law, the position of ἔσεσθε (reversing that of Deuteronomy) shows that still greater emphasis is placed on their “perfection” as something to be attained. Also, while in the parallel passage of Luke the stress is upon the change that must take place (γὶνεσθε) – unless, as is possible, it has the simple meaning “show yourselves” (cf. ver. 45, note) – in Matthew the possibility or even the certainty of attaining it is definitely stated. You shall make this your aim, and shall attain to it. Therefore. A deduction from the principle laid down in vers. 44-47. From the consideration of the example of your Father, and of the insufficiency of being like publicans and heathen. Perfect (τέλειοι). In the Gospels here and Matthew 19:21 only. The word denotes those who have attained the full development of innate powers, in contrast to those who are still in the undeveloped state – adults in contrast to children. Thus the thought here is – Ye shall be satisfied with, and shall attain to, no lower state than that of maturity. But what is it as to which they shall be mature? Surely not the whole Law as illustrated by all the examples since ver. 21; for vers. 31, 32 are excluded by the comparison with God immediately following. It must be the subject with which the sentence is closely connected, vers. 44-47 (cf. Meyer); love to others even though they have done you wrong. In this respect, viz. love to others, you shall admit, says our Lord, no lower ideal than that of’ maturity, even such maturity as is found in him who sends sun and rain on all alike. Some (Augustine, Trench) have seen in this a merely relative maturity, itself capable of further development; but the subject rather demands absolute and final maturity. This does not imply that man will ever have such fulness of love as the Father has, but that he will fully and completely attain to that measure of love to which he as a created being was intended to attain. It may, however, be in accordance with true exegesis to see, with Weiss, for such apparently is his meaning, also an indication of further teaching – the nature of the revelation made known by Christ.

For whereas “the fundamental commandment” of the Old Testament, “Ye shall be holy; for I am holy” (Leviticus 11:44, 45), was the more negative thought of God’s exaltation above the impurity of created beings, our Lord now puts forth “the positive conception of the Divine perfection, whose nature is all-embracing, self-sacrificing love. And in place of the God, for ever separated from his polluted people by his holiness, to whom they can only render themselves worthy of approach through the most anxious abstinence from all impurity, and by means of the statutes for purification contained in the Law, there is on the ground of this new revelation the Father in heaven, who stoops to his children in love, and so operates that they must and can be like him” (Weiss, ‘Life,’ 2:156). The simple and straightforward meaning of the verse, however, is this – You shall take no lower standard in love to enemies than God shows to those who ill treat him, and you shall, in fact, attain to this standard. Upon this (for the limitation of the meaning to one point makes no real difference) there arises the question which has been of so much importance in all ages of the Church – What is the measure of attainment that is really possible for Christ’s disciples upon earth? ought they not to expect to live perfect lives? But the text gives no warrant for such an assertion.

No doubt it says that attainment to maturity – to perfection according to creaturely limits – is eventually possible. That is implied in ἔσεσθε (vide supra).