Every Christian is significant to God and to His people. Each of us has a part to play in building God's church. Even just being here on Sundays, or at other times when Christians meet together, such as home groups, is being a gift from God to the church. We are not independent, but all part of the one body, and as Paul says in verse 26, when one part suffers, the whole body suffers. Look at verse 7 again.
Manifestation is a rather daunting word.
But the manifestation of the Spirit is nothing spooky. It doesn't even necessarily mean supernatural things from God. The Spirit of course is God the Holy Spirit, the third person of the trinity. He manifests himself, not in spooky ways, but in the everyday way we use the gifts He gives to us. Manifestation means clear evidence that something is there.