The meditative state is a special state of consciousness that is quiet and principally devoid of active thinking of any sort. Mantra, focus on the breath etc. are simply the techniques or vehicles used to take you to the edge of the meditative state of mental quiet.
There are a number of mantra meditation techniques alone. Some of them require very rigid focus on the mantra. Some do not. The mantra technique you learn in "Discover Meditation" is a passive mantra technique. Because most people have rather active minds, this mantra technique works best for the majority.
In a passive technique you repeat your mantra a couple of times and then listen for the echo of your mantra to repeat itself in your head. Here's an example... Imagine you are in a great forest or at the opening of a cave on the edge of a lagoon. Now, call out "HELLO"!! Then be silent and listen. You will hear your call return to you as an echo again and again, each time becoming more faint and dim.
With the passive mantra technique you are focusing your attention on hearing that echo for as long as possible. Your mantra will fade sometimes, get louder sometimes, and maybe even disappear for a bit leaving you in silence.
Moments of silence are the edges of the meditative state arising. As you become aware of moments of silence, relax and let your self slip into that state and remain there for as long as the silence remains.
Should you suddenly realize that thoughts have intruded into this silence, simply start listening intently to see if the mantra is still there somewhere, possibly faintly repeating itself in the background and waiting for you to notice it again. This is preferable to an active repetition. But if all else fails, go ahead and give it a repetition or two just to get the ball rolling again, and then go back into passive mode.
Of course, it is possible you may occasionally get carried away with your thoughts and have to actively repeat your mantra a couple of times to clear out all those other thoughts. But having done that, you return back into passive mode. You don't keep actively repeating it.
You don't need to try to be perfect. Just be consistent with your practise and you'll soon realise just how invaluable a few minutes a day slipping into the silence really is. Michael Mackenzie (c)