I haven't taken a poll, but my pretty good guess is that those two questions are very high on the list of things most serious Christians wonder about. Sure, some have heard the still small voice or some variation. But even those wonder later if they are carrying out God's directions correctly. Moreover, even when we are in the middle of very effective work for the Kingdom, we can wonder if it is time to turn that work over so that we can answer God's call from Isaiah 6:8, "Who will go for us?"
We see in the Bible that God can call folks in many different ways, and when they are in various states of devotion. But our chances of being of service seem optimized when we are "after God’s own heart," like David. Jesus doesn't mess around on the subject. He says he wants disciples. Oswald Chambers says this on May 24 in My Utmost for His Highest:
“We have a commercialized view—we count how many have been saved and sanctified, we thank God, and then we think everything is all right. Yet our work only begins where God’s grace has laid the foundation. Our work is not to save souls, but to disciple them. Salvation and sanctification are the work of God’s sovereign grace, and our job as His disciples is to disciple others’ lives until they are totally yielded to God. One life totally devoted to God is of more value to Him than one hundred lives which have been simply awakened by His Spirit. As workers for God, we must reproduce our own kind spiritually, and those lives will be God’s testimony to us as His workers. God brings us up to a standard of life through His grace, and we are responsible for reproducing that standard in others.” (emphasis added)
This process of discipleship, with the associated disciplines, decisions, and sacrifices represent the stepping stones to love of, devotion to, and intimacy with God. The closer we get to Him, the better we are able to discern our Good Shepherds voice, the more we will hear clearly what it is that He would have us do.
Are you ready to respond as Isaiah did with, "Here am I. Send me?" God Called - He Needs Your Decision! was written to help you to that point of surrender.