Tinylily, please tell me where I said reins have no place and are not needed? I don't remember typing or reading that?
I was not going to give her a 100 page lecture on how to engage her horse and get him through, when there are plenty of threads on here to read through that will give her a good idea.
You cannot deny that the hind end is the 'engine room' of the horse, if you don't have the hind end working, the back won't work, the forehand will lead and the neck will be braced. In a nutshell, you havee to activate/create energy in the hindquarters, asking them to step through and under your centre of balance in order to engage the horse's back. The energy you create has to be contained to avoid the horse running onto it's forehand, therefore yes the reins must be utilised, particularly when beginning this work with a horse/rider, to contain the created energy and 'complete' the circuit, allowing the back to free up and the hind legs to swing through. However, the reins are NOT see-sawed, pulled etc. They merely act as a support. A contact is maintained, there should not be a loop in the rein or the contact with the hind legs is broken, however the rein should never be pulled back toward you body. The contact is there to encourage the horse to swing the hind legs and give the back, the horse must be invited to take the contact by riding the back end to meet the contact, rather than riding the contact to the hind end.
In saying this, the seat is more important than the rein in the process of containing built up energy, the core muscles of the rider 'hold' the horse 'together' and 'up', before the reins come into play to give the final, 'finishing touches' to the picture.