I think the meaning here is clear on the first part, to coordinate your body movement (foot, hip, arm, weapon) for maximum power in your blow. You can't "strike then move" or vice versa, after all. The second part on feet against one another could mean literally heel to heel as is known in one kind of quick or false step, or it could be poor wording/translation that means to simply have your feet coordinated so that you pass.
Something you might find interesting from another martial art, Sashinryu. They have a technique called 'star step' in which the moving foot is brought to the nonmoving foot and then moved to the position it's intended to go in, always kept near the ground or even dragged along the ground so that both feet can be put on the ground at any time if needed.
The feet together is an offbalance transitional position but it permits a very wide number of movements from that position to any other, it's less predictable.
There's also somethnig known as the "thief step" or "rogues step", let me do some looking on this. It's walking by bringing the rear leg up to the front one and then moving the front one foward to step - you can test this yourself, the benefit is that your center of gravity remains between your feet at all times.
Unfortunately, footwork is something so basic and critical that these masters probably felt it was common knowledge and so it's not treated in depth, even though really it's the basis of all power =/
Start with yourself.
