Mark the blameless man [who is spiritually complete], and behold the upright [who walks in moral integrity];
There is a [good] future for the man of peace [because a life of honor blesses one’s descendants]. – Psalm 37:37
An upright person is perfect with a perfection of PARTS, though not of degrees. There is no part of them but is embroidered, and bespangled with grace. Though they be sanctified but in part—yet they are sanctified in every part; therefore grace in a believer is called a new person. The work of the Spirit in the heart is a thorough work – grace in the heart is like air in the twilight; there is no part of the air but has some light in it, and in this sense the upright person is perfect.
The terms of blameless and upright, refer to the spiritually mature believer.
More often than not, moral predictability in persons who mature Spiritually is pretty high. Sometimes we are fooled by the hypocrites, but on average, the Spiritually mature are fairly predictable.
There are often serious misunderstandings about the doctrine of perfection. It is often confused with the idea of complete sinlessness, especially as the latter has been seen as a condition to be realised in this life. However, far from being a description of not being something (i.e. sinful), it is an expression of the great spiritual ideal of what we are and should be.
The Most High takes pleasure in those whose conduct is a reflection of their spiritual soundness, their purity, their blamelessness.
Righteousness equals peace. Obedient behavior produces peace and stability.
When a person is in perfection, they are in blamelessness (unblameable, without blame and offence, unreprovable and without rebuke, faultless, and sincere), because they are in the active virtues of salvation which clothe a person in the lawful righteousness of Christ’s sinless perfection; but they are NOT sinlessly perfect by deed until they are finally resurrected at the gospel’s consummation. Therefore also, as a person will be called perfect and blameless, so also they’re called holy and sanctified for the same reasons which stem from their saving connection to Christ. They have inward and immediate holiness and sanctification (by nature, Spirit, and law), and are also, therefore, without blemish and spot in the eyes of God. All of this is because they have been baptized with salvation in the Spirit of God, Whose work is to make us crucified, dead, buried, resurrected, and ascended with Christ.
What is it which distinguishes the one character from the other, wherein lies the difference between the genuine Christian and they who are one in name only? This: a God-given, Spirit-wrought faith in the heart. Not a mere head-knowledge and intellectual assent to the Truth, but a living, spiritual, vital principle in the heart—a faith which cleanses the heart, which working through love, overcomes the world. Yes, a faith which is Divinely sustained amidst trials within and opposition without; a faith which exclaims even though He kills me; I will hope in Him.