This is a verse in which the Bible tells us about the Bible. We learn what place the Word of God should have in our life and what the perils are if it is not.
The first key word is "vision". This reminds us of the source of the Scriptures. Though God used apostles and prophets and holy men to share His message with the world, the words are His. "For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost" (II Peter 1:21). Or, as it teaches in another New Testament portion, the Scriptures are so truly God's words they are declared to be God-breathed.
The word "vision" highlights the fact that Scripture has not originated with man. God sent it down from heaven and committed it to chosen messengers. Often the prophets referred to their message as a vision. "The burden of Nineveh. The book of the vision of Nahum the Elkoshite" (Nahum 1:1). This differed fundamentally from man-made counterfeits. "Thus saith the LORD of hosts, Hearken not unto the words of the prophets that prophesy unto you: they make you vain: they speak a vision of their own heart, and not out of the mouth of the LORD" (Jeremiah 23:16). Not all that glitters is gold in the spiritual world.
The second key word is "law". Often the significance of the word law goes beyond the Ten Commandments to a broader context of Scriptures. It is certainly a word that brings to mind the authority of God's Book. God's Word directs us into the ways of the Lord and is something we are to "keep".
We can easily see the overall message of this verse. Without the active ministry and working of God's Word in the human life, man continues on a road to doom ("the people perish"). And even the life lived on that road is an unhappy existence. What a sad prospect is the life left to itself and untouched by the Word of God - a pilgrimage on this earth marked by basic unhappiness, only to find when life ends the destination reached is unspeakably worse. As the song says, people need the Lord.