I have a philosophy that, any thought or realization that leaves you feeling peaceful is God assuring you that things will be okay, while any thought or realization that makes you feel anxious and worried over something (especially if it’s something ridiculous) is most likely not from God. Anyone else agree?
I claim no expertise on this, that said…
What you said can often be the case, however, sometimes even good angels inspire fear, and fallen angels peace or a kind of peace. Anxiety is usually to be warred against but not all fear is bad, sometime anxiety is even what was first a proper object of fear misused properly, instead of dealt with properly.
The devil can produce peace for evil reasons, and does so at times. As a rule the test for this is of course, whether that peace itself is leading you into a sin – i.e. a peace about some question of morality, feeling peaceful about the error, feeling peaceful about some sensual passion or indulgence, etc.
For example someone praying over the book of Mormon might feel peaceful about it, someone engaged in sexual abuse might feel peaceful about it, someone trying to get God to give an extraordinary inspiration might feel peaceful about it and yet be presuming and sinning by asking for the extraordinary, etc.
Interior peace is very important to maintain so that you stay able to judge rightly and pray to God continually. At the same time there are deceptive spiritual sources for peace.
True peace is cleaving one’s will to God entirely, and a clean conscience. I think that a misleading peace would be changeable and dependent upon having certain things. Prayer brings peace.
You should I think normally not use the spiritual feeling of peace as a way of determining right from wrong, that is presumptuous.
You use the Faith for that… and if the peace is in accordance with the Faith, then it would generally be harmless and beneficial, barring of course extraordinary situations such as a demon simply trying to accustom you to accepting spiritual communication with it.
The Holy Spirit brings peace of mind, and to clear the way for the Holy Spirit we must strive to be pure of heart and free of passions.
I’m no expert, I am no saint, there are likely flaws with what I just wrote, these are just my thoughts on the matter. I hope we hear more from others.