The following excerpt is taken from SACRED THEN AND SACRED NOW - THE RETURN OF THE OLD LATIN MASS by Thomas Woods, Jr., Roman Catholic Books, www.booksforcatholics.com, Copytright 2008. (My emphases and comments appear in bold type.)
The abandonment of this pious practice is of very recent origin - four decades ago it was still the common manner of receivng Holy Communion.
Why shouldn't we receive Christ on our knees - as was (and in some places still is) even the the traditional Lutheran posture when receiving Communion? A parish bulletin insert from several years ago employed a common argument to justify the change: "We should remember that standing itself is a gesture of reverence. It is our cultural custom to stand when a dignitary enters a room or when we sing the national anthem."
[This comment is incredibly ignorant. But I withhold comment because the author says here what I would say.]
To be sure, at some times and in certain places, standing was the posture that indicated the highest form of reverence. But that is not the case in modern Western culture, and so appeals to the practice of the early Church are irrelevant to the situation in the West here and now. It is surely unwise to disrupt traditional Catholic piety for the sake of intruducting a gesture that is less suggestive of the kind of reverence that is owed to God alone, and more suggestive of the reverence we show when a a mere "dignitary enters a room." Jesus Christ is rather more important than the ambassodor from Liechtenstein.
[I would add that this goes for the standing after Communion, and in some places, standing through the consecration as well.]
In practice, having people receive the Eucharist in an ordinary way - we stand all the time, after all - rather than an unusual one (how often do we kneel, except before Christ?) can make them think that what they are receiving in Holy Communion is relatively unremarkable. This principle has often been summed up by the Latin phrase lex orandi lex credendi, which is normally translated as "The law of prayer is the law of belief." How we pray influences what we believe. If the words and postures by which we pray leave some question about the nature of the Mass, the offering of sacrifice, and the Real Presence of Christ, then our belief in these things is likely to grow less certain and more confused.
Cardinal Ratzinger's remarks about the value of kneeling in the liturgy are worth recalling here. Kneeling, he said, "may well be...alien to modern culture," which has "turned away from the faith, and no longer knows the One before whom kneeling is th eright, indeed instrinsically necessary gesture. The man who learns to believe learns also to kneel, and a faith or a liturgy no longer familiar with kneeling would be sick at the core." He also pointed out the numerous biblical examples that emphasize kneeling as the proper posture for adoration and prayer. How appropriate, then, to kneel at the moment of Holy Communion.