If the kingdom is now, why the Rapture?
Why can't it just grow and take over every
thing?

There are various kinds of 'kingdom now'
teachings in the world. The fact is that the
kingdom was rejected by Israel and will
not be established in the world until Jesus
comes in power and glory!

Today God represents Himself in this world
through the [unseen] body of Christ and
through the [seen] lives of the believers.

The kingdom cannot 'grow in the world',
but it will come suddenly and be imposed on
the world by the King, the Lord Jesus Christ.