There is definitely a difference between going out and being sent. The difference is self-determination. Are we directing our own paths or is the Spirit? We can sacrifice anything we want to serve Jesus. We can do whatever we want to serve Jesus. We could probably even do a great job, but is it what the Father wants? It isn't about our sacrifice and what we want. It is always about the Father's will.
I think one of the things that encouraged Moses the most during his leadership of the newly forming nation of Israel was that he didn't choose the job but the job was chosen for him. In the face of every rebellion and every challenge he was able to say, "This is what Yahweh says".
At one stage there was a great rebellion against Moses but Moses did not defend himself. It was always Yahweh that defended him because he was Yahweh's servant. Moses knew what was about to happen to the leaders of this rebellion and he said to the people:
By this you shall know that the Lord has sent me to do all these works, for I have not done them of my own will. (Numbers 16:28)
Basically he was saying, look to the fact of if I defend myself or if I am defended. Moses never said he was worthy of the position but it was well known that Yahweh had placed him in it. During those lonely times of leadership, during the rebellions, during the self-doubt, that single thought must have been his greatest comfort.
Consider Jesus, who did not go out but was sent by the Father. Throughout his ministry he told everyone he was sent to represent the Father and to do his will. Read John 5 for a greater insight into this but in summary I quote:
I have testimony weightier than that of John. For the works that the Father has given me to finish—the very works that I am doing—testify that the Father has sent me. (John 5:36)
Apostle Paul's testimony was also one of being sent. Paul did not wake up one day and decide to join the Church and spend the rest of his life going in and out of jail while telling people about Jesus. He knew his commission and who had commissioned him. Throughout his ministry he was consumed with the desire to fulfil Jesus' will. What a comfort it must have been as a prisoner to know he had not chosen this life for himself but that he had been sent.
We too have been sent but are we submitted to that will? Are we a "take charge" sort of person and do what we feel is best; afterall, Yahweh did create us with a brain. The only problem then is we can find ourselves in difficult places like Moses where self-doubt will destroy us. If we made our own decisions and stand in our own messes we will find it hard to find assurances. It is only when we listen, obey and stand in the confidence of having been sent that we are able to trust that it is all under control. If you have been chosen for the job than the Father has your back. He will provide for you, defend you, give you wisdom and equip you in every way. You need only trust, obey and operate in the authority he has given you. But this confidence is only yours when you know you have been sent and you did not choose this for yourself.