How do you know God wants to speak through your pastor? How do you know God wants you to listen the one preaching in your midst?
The answer is: The Divine Call
God calls men to preach His Word to His people. If they do not have a special call to preach, you should not listen to them. All of the prophets and even the apostles constantly appealed to their divine call when speaking to the people of God.
But wait a minute, all believers are called priests. Do all then have a general call to ministry?
All who believe are indeed priests, but we are not all teachers. As St. Paul writes, "Are all apostles? Are all prophets? Are all teachers?" (1 Cor. 12:29) and again "[Christ] gave the apostles, the prophets, the evangelists, the shepherds and teachers" (Eph. 4:11) St. Peter explains, All Christians are priests, not that all should function without difference in the ministry of Word and Sacraments, without a special call, but that they should offer spiritual sacrifices.
Yet all Christians have a general call to proclaim the Gospel, to speak the Word to one another, to admonish each other in the Word, to reprove and to comfort. Likewise the head of the family is responsible for instructing those within the household. But the public ministry of Word and Sacraments is not entrusted to all Christians in general. It requires a special or particular call. As St. Paul writes, "How are they to preach unless they are sent?" (Rom. 10:15)
Ok. How then does God send men to preach? How do we know God has called the preacher in our midst?
Certainly God has immediately called men to preach in days gone by, such as the prophets and apostles. But in these last days He calls men to preach mediately - through the ministry of His Church to whom His has given His Word and Sacrament. Timothy is the perfect example of this. He was called through Paul and the other pastors. He also received the mandate to do this when appointing other ministers in the Church.
So this is how you know - when a Christian congregation, one that seeks to gather around their Lord in His Word and Sacrament, calls a man to fill this Office of the Ministry in their midst and deliver the Lord's gifts to them. This called man, called by the Lord through His Church, is the one God has sent to publicly preach.
What a comfort! A Christian congregation entrusts themselves to the Lord in sending them a preacher, and He works through their call to legitimize the ministry in their midst. Thanks be to God that He sends preachers to deliver all that His Son accomplished on the cross.