Try not to think not of getting him "on the Bit", but of putting your hands within reach of the horse's mouth. The horse will automatically seek the contact.
However, the horse will only attempt to make contact, if your calf aids ask for the hind legs to step up and the seat aids channel the movement forward towards the bit. In other words, you -the rider - have to make your hands available for your horse, that's all.
You cannot do this with the reins on the buckle - there must be a connection.If the reins are on the buckle, there is no way the horse could ever reach them, unless he stretches all the way forward and down. This stretching is valuable and desirable, of course, but not all the time. There is a time for stretching forward-downward and there is a time for arching and elevating the neck out of the withers.
The difference is communicated to the horse by your seat and legs. Think of the bit as being the forward-most point of your seat - but your seat must be stable, balanced, and connected for this to be able to happen. This means having the elbows connected to the seat too. They must hang off vertical upper arms and rest lightly at your sides. The whole arm (shoulder, elbow, wrist and finger joints) must 'breathe’ with the horse's movement. Otherwise the bit is just a separate piece of equipment whose influence is limited to the mouth alone.
But the bit’s action is not just limited to the horse’s mouth. If your seat is connected everything done with the bit travels through the horse’s whole body. You can use the reins to monitor imbalances. For instance; you can learn to feel blockages in the poll, jaw, neck, shoulder, back and even hind legs. You should, literally be able to feel your horse’s hind hooves in your hands and this pattern continually recycles itself from hoof to hand via the seat, legs back, etc. If there are muscle tensions somewhere along the line this recycling of energy will become broken (it will short out) and you won’t feel the whole horse working ‘through’.
Durchlässigkeit (throughness) is only possible on a horse whose back is moving in a supple swinging manner. If you can’t feel the impulse of the hind leg in his hand, it is because there is tension somewhere in the horse's body. The horse has to step freely into the bit with his hind legs.
When you get this feeling in your hand, you know you are on the way to achieving an elastic contact and having your horse "on the bit".
If there are any points you want to ask me about, please feel free to ask questions.