We are like soldiers who, however long they have served, must always be ready for their captain to send them away on any duty which he wants to entrust to them, since it is he who is paying them (St Theresa, The Way of Perfection).
At first glance we think that there is a big difference between Jesus' calling people to be apostles and recruiting to the army. But Saint Theresa is not afraid to name even her sisters in the monastary soldiers. She encourages them to trust more and not to worry about the future. For her vocation is like a struggle but it is worth it.
The standard-bearer is not a combatant, yet none the less he is exposed to great danger, and, inwardly, must suffer more than anyone, for he cannot defend himself, as he is carrying the standard, which he must not allow to leave his hands, even if he is cut to pieces.
Saint Theresa goes further and compares the God's beloved to special soldiers who are in great danger. They have to suffer a lot with patience standing by the faith and keeping her strongly in their hearts. Sometimes it seems that following Jesus is easy and not demanding. But the reality is that listening to the God's words and fulfilling our duties is always difficult. Therefore, first Jesus calls us to be fishermen and later when we are advanced to be his soldiers.