Thanks for your question; countless Christians probably are wondering the same thing!
When preaching from the Old Testament, one must remember some foundational principles that apply to _any_ passage, not merely to the prophetic sections of Scripture:
1. All of the Scriptures, Old and New, testify to the Lord Jesus Christ (St. Luke 24:27). If a sermon from the Bible does not bring Christ to bear on the passage, then it is not a true, biblical sermon. For example, a sermon on the days of creation would be deficient if it did not also mention St. John 1 and the creative work of the Eternal Word, Jesus Christ.
2. Therefore the New Testament (which, obviously, reveals the Christ more clearly than does the Old) interprets the Old. The writers of the NT understood this fact: see St. Matthew 1:22-25 and Romans 9:25ff, for example.
3. Still, the Old Testament texts deserve to be studied _in situ_: that is, in their own context first. An example: what did it mean for David to cry out (in Psalm 22), "My God, my God, why hast thou forsaken me?" And what did it mean for David's Son and David's Lord, Jesus, to cry the same thing from the cross?
(Some Old Testament texts, such as Psalm 110, seem to point to the Lord Jesus Christ directly without any local referent -- but in general, Old Testament passages can and should be studied first in their own setting, and then related to Christ).
Turning more specifically to your question, it is vital that we define "prophecy" in a biblical sense. If they were honest, most Christians would define prophecy in this manner: "Prophecy is that part of the Bible, both Old and New Testaments, in which God tells us what's going to happen right before the end of the world."
That is a _popular_ definition of "prophecy;" unfortunately, it is incorrect!
In Scriptural terms, a prophet is one who declares the Word of God. That's it! Certainly, those prophecies sometimes contained a "future element." But often in the Old Testament, a prophet prophesied a "future prediction" along these lines: "If you (God's people) repent and turn back to the Lord, He will spare you; but if you continue to rebel, He will judge you" (see, for example, Jeremiah 22:1-5). Remember, God's unifying purpose in all of human history is to bring glory to Himself by purchasing for Himself a holy, faithful people from all ethnicities (Ephesians 1:4). God did not commission the prophets of the Old Testament to predict the end of the world for the Jews of that day and for us today; He commissioned His prophets to call people to repentance, to faith in Him and to obedience to His Word.
Jesus perfectly fulfilled the role of prophet, in that He was _and_ declared the Word of God for humanity. And while the sort of prophecy of the apostolic era has ceased (I Cor. 13:8), true preachers of the Word can be considered prophets today as they correctly and faithfully interpret and apply the Scriptures to God's people.
So when this minister preaches from the Old Testament prophetic books, he bears a few guiding principles in mind:
1. What did the passage mean to its original audience?
2. How does this passage find its fulfillment in the person and work of the Lord Jesus Christ?
3. What does it mean for God's people today?
Let me also state that only the last 2.5 chapters of the book of Revelation (20:7-22:21) have yet to be fulfilled (the Day of the Lord [the second advent of Jesus Christ] and the subsequent ushering in of the New Heavens and New Earth). This means I do not read a passage from Isaiah and immediately ask, "What does this text say about the end of the world?" Such might be a popular approach to the OT prophetic books, but it is irresponsible, misleading and regrettable.
The Old Testament prophets tell us a great deal about God's might, holiness, mercy and will. As His redeemed in Jesus Christ, we would be wise to take their challenging words to heart and to ever live near to our Lord, that we might truly be His people (I Peter 2:5).
Thank you again for your thoughtful question!