Prayer is the life of the soul.
Food and rest are essential to sustain human life; knowledge, art, and culture in general enrich the mental capabilities of men, but only prayer reveals and expands our spiritual faculties.
God loves all of his creation, and in particular he loves each of us. As it is natural for a child to want to see and converse with their parents, so it should also be natural and pleasant for us to converse with our Heavenly Father and to want to be in spiritual communion with him.
This conversation with God is called prayer.