Actually, the current version of the NASB has this translation:
Therefore, all who are mature, let’s have this attitude; and if in
anything you have a different attitude, God will reveal that to you as
well;
[The OP appears to be quoting an older edition.]
The operative word here is τέλειος (teleios) which BDAG defines as follows:
- pertaining to reaching the highest standard, (a) of things, perfect, eg, James 1:4a, 17, 1 John 4:18, etc
- pertaining to being mature, full-grown, mature, adult, eg, Eoph 4:13, 1 Cor 14:20, 2:6, Heb 5:14
- pertaining to being a cult initiate, initiated, eg, Phil 3:15, Col 1:28
- pertaining to being fully developed in a moral sense
- (a) of humans, perfect, fully developed, eg, James 3:2, Matt 19:21, 5:48a, James 1:4b
- (b) of God, perfect, eg, Matt 5:48b
Given these shades of meaning of this word τέλειος (teleios), it is arguably a poor choice to imply that the meaning in Phil 3:15 is simply "perfect". As the most recent edition of NASB suggests, "mature" might be a better translation. Other versions often have something similar:
- NIV: mature
- NLT: spiritually mature
- ESV: mature
- BSB: mature
- BLB: mature
- NKJV: mature
- Amplified Bible: mature [pursuing spiritual perfection]
- CSB: matuire
... and so forth. Ellicott offers these comments about Phil 3:15 -
(15) Perfect.—The word is apparently used with a touch of irony
(as perhaps the word “spiritual” in Galatians 6:1), in reference to
those who hold themselves “to have already attained, to be already
perfect.” It is, indeed, mostly used of such maturity in faith and
grace as may be, and ought to be, attained here (Matthew 5:48;
1Corinthians 2:6; 1Corinthians 14:20; Ephesians 4:13; Colossians 1:28;
Colossians 4:12; Hebrews 5:14). But, strictly speaking, this life, as
St. Paul urges in 1Corinthians 13:10-11, is but childhood, preparing
for the full manhood, or “perfection” of the next; and his disclaimer
of perfection above suggests that this higher meaning should in this
passage be kept in view. The prospect of being “perfect” in
indefectible faith or grace is the Christian’s hope; the claim to be
already “perfect” is always recurring in various forms—all natural but
unwarrantable anticipations of heaven on earth. St. Paul, by a
striking paradox, bids those who hold themselves perfect to prove that
they are so by a consciousness of imperfection. If they have it not,
he says, they have something yet to learn. “God will reveal even this
unto them.” The conviction of the Holy Ghost unites inseparably the
“conviction of sin” and the “conviction of righteousness.” The
“judgment” of absolute decision between them is not yet.