Many who fail or continually make mistakes in ministry or service at some point in their lives must feel miserable, thinking that they're inadequate for the task that God has given them. As much as I'd like to say "you can do it," my friend, the best thing that I could tell you is this: "Apart from Christ, we're nothing."
Inadequate for the task
All of us will be unable to do what God wants us to do if we are without Him. Trying to do things in our own strength and expecting God-sized outcomes will even be more painful. This is simply because no human can ever do the will of God without the strength that God provides, and no good success could ever be achieved without the goodness of God being involved. This is because it's in Him that we live, move, and have our being (see Acts 17:28).
Every good thing
We have to realise that everything we have achieved or will achieve can only come through the grace of God. James 1:16-17 tells us, "Do not be deceived, my beloved brethren. Every good gift and every perfect gift is from above, and comes down from the Father of lights, with whom there is no variation or shadow of turning." This is the plain truth.
Every success that we have comes from God. The strength with which we fought for that achievement also came from God. Deuteronomy 8:18 tells us, "And you shall remember the Lord your God, for it is He who gives you power to get wealth, that He may establish His covenant which He swore to your fathers, as it is this day."
More than that, we will be unable to do anything for God if we aren't rooted in Him and getting our nourishment from Him. The Lord Jesus clearly said this in John 15:4-5.
"Abide in Me, and I in you. As the branch cannot bear fruit of itself, unless it abides in the vine, neither can you, unless you abide in Me. I am the vine, you are the branches. He who abides in Me, and I in him, bears much fruit; for without Me you can do nothing."
Why you shouldn't feel inadequate
My friend, although we are nothing without Christ, the truth also includes the other side of the coin: if we are in Him, abiding in Him, and are relying on Him, we have all that we need. Philippians 4:13 states, we "can do all things through Christ who strengthens" us.
So ask yourself: are you in Christ? Are you relying on Him and the strength that He gives, not in in what you have in yourself? If you are dependent on Him, there's no reason for you to feel inadequate. You are more than a conqueror in Christ (see Romans 8:37) who gives you strength and grace.
