There is no limit to what God can do. Anything a believer could think, dream, ask, or pray for God can surpass. The way God can do that is through His power at work inside the believer. There may be people that feel they are not strong enough, educated enough, or bold enough to complete the calling on their lives.
Scripture shows this is true, they are not good enough. God, however, can do all things!
If the believer accepts the Holy Spirit, He will give them the capacity to be effective in the world. If one simply has faith, God can do incredible things through them which will bring Him glory for ever and ever.