Genesis 6:22 (KJV)
Thus did Noah; according to all that God commanded him, so did he.
I have friends who are both ministers in their church, and work a public job. It surprises me when they see their public work as less important than their ministry. I see BOTH vocations as ministry. I see the public job as God paying them to work in His harvest field. The duties of the church must be done as well. But that is a very closed-off role.
The passion and drive to be full time in ministry is a noble one. It may even be of God, in order to keep us in both fields. If we didn't have the drive for ministry we'd surely give in to the exhaustion at the end of a workday. And it's likely that the blessings and favor of God would not be on our public job if we weren't giving so much to our ministerial job. Regardless, we do have that higher calling of ministry, so tired or not, we do our church "job" after our public one.
Our first leanings to "knowing" we're hearing God's voice is if the instruction is "spiritual." I mean, if the instruction is something like, "Pray," or "Fast," or even gifts of prophecy. But we should not discount that God has always worked through "carnal" means as well.
God gave Noah detailed instructions about a boat. A BOAT! What in the world is "spiritual" about a boat?! God didn't give him prayer guidelines. God didn't tell him how or why to fast. God didn't tell him to convince others to join him in salvation. He just told him how to do a very physical, natural thing.
I feel certain that he did, in fact, pray and preach. (The New Testament calls him a "preacher of righteousness.) But what God told him to do was a very flesh and blood, wood and tar thing. He was not alone, Paul and other New Testament ministers had bi-vocational ministries as well.
Don't quit your day job. God is using the bi-vocational minister more and more.
Don't think that college is "not ministry." Don't assume that being a hostess in a restaurant, or a construction worker, or a lawyer, or whatever your non-ministry job may be, is "non-ministry." There is likely more ministry happening there than in the church.
There are some who will take on the church full-time. Their efforts to make sure their hands are "dirty" from working in the harvest is HUGE. When working full-time in the church, it's easy to spend weeks without bumping into a single person who needs Christ. (Or who realizes they need Christ.) Granted, having music, and the spoken Word polished and ready for saint and sinner in a church service is paramount. Being available to go pray when the sick call for an elder is integral. The mechanics of church administration is a full-time job. But full-time church work is not all it's cracked up to be.
Do not underestimate the importance of where God has you in bi-vocational ministry.
It's a very spiritual carnality.