night and day praying exceedingly that we may see your face and perfect what is lacking in your faith?"
1 Thessalonians 3:9-10 (NKJV)
One of the first jobs I had was working in a store that sold auto parts. Our store would be contacted by someone who was repairing a car, because they were missing something that was needed to complete their work. These people that needed the parts were usually auto mechanics, and they called us to bring the necessary parts to them. My job was to then deliver those parts to the mechanics so they would be able to do their job and finish their work.
In 1 Thessalonians 3:9-10, Paul said the Thessalonians needed something to “perfect”, or “complete thoroughly”, their faith, and Paul said he would bring what they lacked. This is similar to what he said in Romans 1:11, where Paul said he wanted to impart to the people in Rome a spiritual gift so they would be established. This shows us that there can be areas in our life and relationship with God where we can be missing some things. This also shows us that God can use someone to bring to others what they may be missing in their faith.
If something is complete it is not missing anything, but if something necessary is missing, then that part needs to be found and put into its proper place. God wants mature believers who are not lacking the things that they need to do the work He has planned for them to do. We should all look for opportunities to take the abilities, knowledge, and wisdom that we have from God and bring that to others to help provide them with whatever they may be lacking in their faith. Whatever it is that God has given us can be used to help others.