That which is wrong under one circumstance, may be and often is, right under another. God said thou shalt not kill,–at another time he said thou shalt utterly destroy. This is the principle on which the government of heaven is conducted–by revelation adapted to the circumstances in which the children of the kingdom are placed. Whatever God requires is right, no matter what it is, although we may not see the reason thereof till long after the events transpire.
(The Personal Writings of Joseph Smith, compiled and edited by Dean C. Jessee, 507-509.)
The above quotation suggests to me that we cannot predict, neither based on our previous experience nor based on our own reasoning, what God will require of us. We may appeal to scriptures regarding God's “unchanging nature,” but it seems that we cannot rule out much, if anything, based on such an assertion. How can we claim that any act of God would be inconsistent with his revealed nature, if we do not “see the reason thereof till long after?”
How, then, are we to distinguish between something that is inspired of God and something that is not?
It seems that our faith and trust in God cannot merely be based in our ideas about him. It cannot simply be based in the idea that he is omniscient or omnipotent or wise or loving, because these things alone are not adequate predictors of what he may inspire -- in fact, there may not be any such predictors. In other words, we cannot say, when confronted with an “inspiration:” “God would never require such a thing!”
How can we trust such an unpredictable God? I think we can only do so when we have a real, meaningful relationship with him: when we feel his love and learn to recognize it in the same way that a child recognizes his mother's voice: “I would that ye should remember to retain the name written always in your hearts, that ye are not found on the left hand of God, but that ye hear and know the voice by which ye shall be called” (Mosiah 5:12). It is God's love and our relationship wih him that is the foundation of our trust, not our intellectual understanding of his character and attributes.