When I told my professional friends that I was leaving veterinary medicine to discern a vocation to the priesthood, their comment was often, "That would be a good second career choice for you. I can see you as a priest."

Their affirmation certainly had a positive influence on my discernment, but I always felt a little unsettled about their assumption that being called to the priesthood was something I could control by my own choice. It's hard to explain it to a bunch of good scientific minds, but it's important that I try, because we all have a vocation call of one kind or another.

In business and life, we make decisions - we choose things - based on external facts. What medicines would help treat what disease? Which piece of equipment and which new staff members would fulfill the needs of my clients and be a positive influence on my practice?

Inside our family, we made choices as to what car to buy, where to send the kids to school and even what to have for dinner. We chose cars for functionality, cost and style. Kids went where they would get the best education. Our budget, time and tastes were considered when we chose our meals. Choosing well was a matter of weighing the costs and the benefits. Success and failure was closely tied to what we chose to do.

We are all familiar with the idea of making moral choices, of choosing good actions because we hear God speaking through our conscience, telling us the right or wrong thing to do. The whole of human history is tied up in what each person who has ever lived has decided to do: Will we listen to God or not? Healthy habits or bad, happiness or pain, kindness or cruelty and war or peace are closely tied to what we choose to do.

But choosing what we will do in a particular situation is an entirely different matter than discerning who God is calling us to be. We get to make our own moral choices and live with the consequences, but it is God who chooses each one of us for our particular vocation, our role in life.

God made each of us with a specific vocation in mind. Granted, we can choose either to listen for God's call or not; and if we have listened and heard, we can still choose to respond or not. But we do not get to determine who God specifically calls us to be in this life.

The idea that God made each of us with a divine plan in mind for us means that we are part of something much bigger than any one of us. The whole process of discernment is about our listening for the call of God and responding to it so that we might become the instrument God wants us to be. It is not about us telling God who we think God ought to want us to be.

Discernment is not a quick or efficient process. It takes a great deal of vulnerable soul-searching. But there is a certain peace that comes with having cooperated with the Holy Spirit and making the choices that God intends. On a moral level, doing good rather than bad brings a sense of peace. Bringing joy where there is sorrow, light where there is darkness, healing where there are wounds - all bring about a sense of peace.

In a vocation to married life, falling in love - real, selfless love, where we want what is best for another before we care about ourselves - brings an overwhelming sense of peace. Being a parent staying up at night with a sick child may be hard, but it brings a sense of peace.

In hearing God's call to religious life, I have found that same sense of peace. Discerning each of our vocations is about being open to God's magnificent, mysterious plan, not our smaller designs. It is really about trusting in God's ability to choose more than our own.

(Mr. Lesser is a widowed father of three and a former equine veterinarian now studying for the priesthood for the Albany Diocese at Blessed John XXIII National Seminary in Weston, Mass. Read previous "seminarian's diary" columns at www.evangelist.org.)