We withdraw our attention from the things of the external world. We concentrate our mind upon some interesting subject. We analyse this subject into all its parts and study these parts and their relations with each other and with the whole of which they are parts. We hold the pattern of the whole analytical process together in an act of comprehension of its meaning. This is called contemplation.
Concentration means 'with one centre'.
It requires that we set up in the mind some single idea of such a kind that to it we can refer every other idea that we have. Such an idea gives us the power of unifying our mind, and so of bringing it into peace and harmony. Our mind compares ideas, notes their similarities and differences, grouping them together in patterns. It is precisely the discovery of a meaningful pattern that is the object of meditation. Contemplation, unlike meditation, does not follow a sequence of ideas through time.