I've noticed something while reading through the Bible. Anytime that someone was called to do something for God, they had some sort of protests. God would tell them what their task would be and they'd throw in a big but.
You can see this in Moses who was called to free the Hebrew people from Egypt. He said BUT who am I to be able to do this? What if they don't believe me? BUT I am not eloquent, I don't speak well.
You can see this in Sarah who was told that her and Abraham would have a child. She said BUT I'm too old to have children...and my husband is too old.
You can see this in Jonah as he was called to go speak at Nineveh. He said BUT they are bad people, they aren't going to listen to me.
There are many examples throughout the Bible of people who had some sort of interjection when they were called to something. We can even see this in our everyday lives. How often have you felt led to do something and you end up talking yourself out of it?
I personally have done this many times. I feel called to write Christian Children's books and of course I say "BUT God, I don't have a theology degree. I'm just self taught. What if I lead someone the wrong way?" BUT I have horrid social anxiety, there's no way I can speak to people to promote a book.
There are people who are called to start some sort of ministry or join a ministry and they always have a BUT because sometimes God's vision is bigger than we can wrap our minds around. We can't see the bigger picture. We only see the obstacles that are directly in front of us. We see the impossibilities.
Of course we know, all things are possible with God. He knows the path, He knows the end result. He will help the people through what he calls them to do. When He called Moses, He knew the path that would lead to the exodus of his chosen people and he equipped Moses for it. When He called Sarah, He knew the path that would lead to Jesus and our salvation and he made her able to carry a child.
When He calls us, everyday modern-age people, to do great things...He knows what we'll encounter and what our shortcomings are. He knows what He'll lead us to overcome and He knows the end results. Trust in that. Don't listen to our buts and instead build on trust. Take that trust fall because he'll never let you fall.