Oswald Chambers' My Utmost For His Highest is one of the most popular devotionals ever complied, and a favorite of mine that has never ceased to kick me in the gut when I'm needing it or feeling a little stale. One of the entries that has always jazzed me up is "Called By God" which looks at Isaiah 6:8, one of my favorite sections in Scripture, and one that's often used for people's calls to ministry.
Those verses are awesome for so many reasons. We see the Glory of the Triune God, a glimpse at the throne room, Isaiah's realization of his iniquity and God's reconciliation for it right then and there. But in the context of this devotional and this post, we see Isaiah answer God's call. To me, one of the greatest things about having a relationship with God and realizing our call to be used to bring others into relationship with Him, is the extreme balance of both our severe insignificance and God's overwhelmingly infinite love for us. This has a lot to do with my personal attitude and feeling when it comes to my call into vocational ministry. It is unbelievable that I'd be chosen, but at the same time not, because the call to join our Father in the Ministry of Reconciliation is there to all who have Faith in Him (2 Corinthians 5:11-21).
Chambers points out that God was not directly addressing Isaiah in His questioning for a messenger. He makes an interesting point that the call is an open general call for all who's spiritual condition is attuned to hear the call. Scripture tells us that we are all called to the ministry of reconciliation, we are all commissioned to go and tell of the Good News (Matthew 28:18-20), and that those who are in the faith are of the holy and royal priesthood (1 Peter 2:5, 9). So yes, as believers we are all called, but God is not knocking down your door because you're some special cog in the Gospel machine. This has many significant implications though, so don't think this is any sort of diminishing of your personal call. If this call was overtly hinged on us individually, then it would give us something to boast about personally, which would be theologically incorrect, since salvation is not of our doing so that no one can boast (Eph. 2:8-9) as well as God's decision to use us despite our brokenness (2 Cor. 12:9), and as previously mentioned all believers are called. Also everything about being a Christian and a minister of the Gospel is about personal humility, by making much of God and His glory and putting others above ourselves in service (John 3:30, Matthew 22:37-40, Phil 2:1-11).
To wrap up, so far I've been applying this to large, all encompassing calls, but I think we often overlook the daily and spontaneous (though divinely ordained) call we have to not only die to ourselves, but to respond to the promptings of the Holy Spirit. Everyday we are in contact with people who we can have the opportunity to minister too, both regenerate believers, and those non-regenerate and outside the faith. The verses in Isaiah, as well as the point that Chambers makes, are for particular calls to specific people, times, and places as the Lord sees fit to use them.
I'm a big advocate for zeroing in on the specific circles of influence that God has ordained you to be in, that only you fit into with the unique position and circle cross-overs that naturally happen. Like a ministry audience Venn Diagram, uniquely ordained by God that we will surely miss capitalizing on if we are not in tune with the Holy Spirit's guiding prompts in our daily lives. Boiling down Isaiah's call in this instance and not just focusing on the incredible nature of the situation with the seraphim and the burning coal, Chambers summarizes "Isaiah was in the presence of God, and he overheard the call." This is how we can be led in the moment to ask certain questions that get at the heart of the matter with someone we are ministering to, or quote certain verses, or do certain things like stopping in that moment to lay a hand on them and pray.
This is the simple take away: There is a call to all believers; as a believer you are called; and to hear the promptings and answer the call, you have to be in His presence; you have to be close to listen.