Why 'under construction'? The verse quoted is from the letter to the Corinthians, a church so divided, so concerned with identity of self rather than an identity with the Lord, that Paul felt he had to sternly remind them in whom they believed; themselves or God. Paul goes on to say that the planter and the one who waters are doing the same thing, serving in the same way; that we are all workers, of the same building.
Paul encourages them that by God's grace the foundation has been completed and that we are to build on that foundation; he reminds them and us today that that foundation is Jesus, the Christ. He closes this thought again warning them and us to think twice about how and with what we build upon this foundation, and that we are that building; the temple of the Holy Spirit.
So we are all 'under construction' and we must follow the blueprint of God, His Word, Jesus, and as Paul, as wise builders, build each other up with the word. When anyone has a question, believer or unbeliever, we turn to the foundation of the word. If you are concerned that you don't understand the word enough (or at all), that you messed up and put the window in the wrong place or the door is crooked; it's okay, because God's grace laid the foundation, we are all 'under construction', join us as we build His church together.