True meditation is characterized by a state of openness and receptivity. But in such a state, the mind is vulnerable to assault by any passing thought that wishes to colonize it. For this reason, meditators are usually advised to do is to take a single element: a mantra, the breath, or a quality, and to “concentrate” on it so that the mind will be occupied with this one thought instead of by all the others.
Nevertheless, the mind remains severely susceptible to attack by so many other thoughts that try to hijack one’s meditation. Eventually, it either gives in and goes with the flow, or enters into a kind of numbness.
So really there is no substitute for a chaste, clear consciousness that can remain completely receptive and vulnerable, but is still able to rebuff, without any resistance, every attempt to seduce it.
If the latter seems impossible, this explains why meditation is only one part of spiritual practice.