Two related verses in Job seem to place God in an unexpected relationship with his angels:
'He puts no trust even in His servants; And against His angels He charges error.
Job 4:18 (NASB)
Is the verse telling us that good angels who did not fall are not good enough.
Behold, God puts no trust in his holy ones, and the heavens are not pure in his sight;
Job 15:15 (ESV)
Why does God have no trust to his angels? Why are the heavens not pure in God's sight?
The answer to your question would seem quite simple.
Since Job 4:1 identifies the speaker whose statement is found at Job 4:18, as Eliphaz:
Then Eliphaz the Temanite answered and said,
and Job 15:1 identifies the speaker whose statement appears at job 15:15, as the same:
Then answered Eliphaz the Temanite, and said,
and God says to that man at the conclusion of the story:
... My wrath is kindled against thee, and against thy two friends: for ye have not spoken of me the thing that is right, as my servant Job hath.
-- Job 42:7 (KJV)
then a prudent reader would suspect the views of Eliphaz are flawed.
One can trust the words of Eliphaz in regard to God's angels and the heavens, or one can trust the words of God who said Eliphaz had "not spoken of me the thing that is right"?
As for me, I stand with God.
First, that we are trying to figure out a spiritual truth intelligibly. That will lead nowhere but to error.
Also, the Bible does not say that "God distrusts His angels". The Bible says that "behold, he put no trust in His servants, and His angels He charged with folly".
Well, every of God's creation is His servant. Whether "righteous" or "unrighteous". We see God calling a heathen king His servant (Cyrus). And Jesus Himself asserted the position of the Godhead over the fallen man in John 2:24.
But after we rise past this position (old man, servant) we become sons and friends. For this new status, trust is achievable.
I'd like to point out the use of past tenses... he put, not the rather present continuous he put's' we are trying to unconsciously but truly attach there. The same applies for and charged His angels with folly. Past tense. This leads to believe that the angels being referred to here are the folk who left their estate for the sake of the daughters of men and the folk who joined the great deceiver in the ancient mutiny of Zion.
God bless us all!
Why does God have no trust to his angels?
The Book of Job does not provide a portrait of God's mind that is comprehensive or detailed enough to allow identifying God's specific reasons(s) for putting no trust in his angels.
What one can answer, though, is whether God's distrust in his angels is epistemologically and factually supported (as per the narrative in chapters 1 & 2). And the answer is in the affirmative, notwithstanding that God's distrust in his angel(s) is notoriously inconsistent: In line with one of the comments, God actually trusted Satan at least twice to unjustifiably harm Job under pretext of the wager between God and Satan.
God's concept of Job was that of "a perfect and an upright man" (Job 1:8, KJV). Satan was given the opportunity to prove that Job's devotion to God is conditional on profit. Satan's proposition turned out to be wrong, for "[i]n all this Job sinned not, nor charged God foolishly" (1:22) and "[i]n all this did not Job sin with his lips" (2:10). Thus, it was epystemologically correct for God to distrust his angel.
(Apropos of --and contrary to-- the other answer, this epystemological accuracy validates Eliphaz's declarations in 4:18 and 15:15, whence one cannot categorically state that Eliphaz's views "are flawed").
Why are the heavens not pure in God's sight?
Without foreclosing alternative explanations beforehand, the Tanakh might shed light on the latter half of 15:15:
The וּ appended to זַכּ֥ suggests allusion to His purity (זך: pure), whence I posit that the clause could be paraphrased as: And in His eyes, the heavens are not [at the level of] His purity.
Thus, rather than labeling the heavens as impure in themselves, the intended meaning of 15:15 might be to expresses God's superiority over any thing (or something) He has created: in this case, the heavens.
