Charles Spurgeon Commentary Genesis 15:12

"And when the sun was going down, a deep sleep fell upon Abram; and, lo, a horror of great darkness fell upon him." — Genesis 15:12 (ASV)

He had asked for a manifestation, a sign, a token, and, see, it comes in the horror of great darkness. Do not be afraid, beloved, if your soul sometimes knows what horror is. Remember how the favored three, on the Mount of Transfiguration, feared as they entered into the cloud; yet it was there that they were to see their Master in his glory. Remember what the Lord said to Jeremiah concerning Jerusalem and his people, They shall fear and tremble for all the goodness and for all the prosperity that I procure unto it.

That is the right spirit in which to receive prosperity, but as for adversity, rejoice in it, for God often sends the richest treasures to his children in wagons drawn by black horses. You may expect that some great blessing is coming near to you when a horror of great darkness falls upon you.