Daniel 7:28 (ESV)

28 “Here is the end of the matter. As for me, Daniel, my thoughts greatly alarmed me, and my color changed, but I kept the matter in my heart.”

Daniel sees how devilishly dangerous this time is for Christ’s church. This is why he experiences such fear. He knows that the Lord saves, and yet he realizes how difficult this time will be for God’s people. This is why he turns pale. He keeps the matter in his heart, in the same way as Mary kept the words of God in her heart, see Luke 2:19, Luke 2:51. It is also important for us to keep God’s words in our hearts, see e.g. Luke 11:28 and Revelation 1:3. This is important for when difficult times are experienced, because we can then go back to God’s promises, and build our trust and hope on them.