Practically everybody receives Holy Communion nowadays at Mass. Do they receive the Lord merely out of habit? Do they seriously understand what they receive? Let me relate to you some of the things St. Teresa says about reception of the most Blessed Sacrament in Chapter 34 of her The Way of Perfection.
She advises that we don't lose so good an occasion for conversing with God as is the hour after having received Communion. We should strive to leave our soul with the Lord ~ he is within us. This is a good time for him to teach us and for us to listen to him. Since you have the Lord himself present, strive to close the eyes of the body and open those of the soul and look into our heart. And he will reveal himself to us. [I would like to vouch for the fact that I made the most spiritual gains during the time I shared my heart with the Lord after receiving him in the Holy Eucharist. On the average, I spent about 40 minutes each time.]
Teresa continues. His Majesty lets all those who love and desire him greatly know that it is he who is present in the most Blessed Sacrament; these are his true friends. Whoever is not his true friend will never trouble with requests that he reveal himself. Such a person will hardly have fulfilled what the Church requires when he will leave and quickly forget what took place. Thus, such a person hurries on as soon as he can to other business affairs, occupations, and worldly impediments so that the Lord of the house may not occupy it. [This is worse than not receiving the Lord.]