Excerpts from Impressions, by Martin Wells Knapp, 5

Good Reading. Good books and papers are among the mightiest agencies which God is now using to impress men with His truth. Through them He is silently undermining the fortifications of the enemy, and building up His spiritual kingdom. They have won many who were impervious to all other appeals, and their influence is mighty and quiet, like the laws of gravity.

Angels. Impressions from above often come from holy angels.

The Psalmist declared that "The angel of the Lord encampeth round about them that fear Him, and delivereth them." These, and many parallel passages in the Word are confirmed by the express declaration in Hebrews that "they are all ministering spirits sent forth to minister unto them who shall be heirs of salvation."
Wise, mighty, holy, elect and innumerable, they are among the most powerful, yet unseen and often unappreciated agencies God has given to "have charge" over His people. Sometimes their special errand is to comfort in some fiery furnace; or to cheer in some dark lion's den; or to warn of some threatening peril; or to deliver Peter from prison; or rejoice over souls newly saved; or to announce the tidings of a Savior's birth and resurrection; or to execute the judgments of God upon the ungodly; or to influence a preacher's appointment, as with Philip; or to help a seeker to obtain the gift of the Holy Ghost, as with Cornelius; or to cheer in danger and point to a promising future, as with Paul. In every instance they have human interest in their keeping, and doubtless much more frequently than is generally thought are the agents of impressions from above.

From Impressions, by Martin Wells Knapp. Original publication date, 1892. Public domain. My source is here. The previous post in the series is here.