We see in the first place genuflection, which is done "by bending the right knee to the ground, signifies adoration, and therefore it is reserved for the Most Blessed Sacrament, as well as for the Holy Cross from the solemn adoration during the liturgical celebration on Good Friday until the beginning of the Easter Vigil." (General Instruction of the Roman Missal, No. 274). The bowing of the head instead means reverence and honor. In the Creed -- except in the solemnity of Christmas and of the Annunciation (Incarnation), in which it is replaced with genuflection -- we carry out this gesture pronouncing the wonderful words: "By the power of the Holy Spirit he became incarnate from the Virgin Mary, and was made man."
Finally, we would light to highlight the gesture of kneeling at the moment of the consecration and, where this use is kept, at Communion. They are strong signs, which manifest the awareness of being before someone special. It is Christ, the Son of the living God, and before him we fall on our knees.
In kneeling, the spiritual and physical meaning form a unity, because the bodily gesture implies a spiritual meaning and vice versa, the spiritual act calls for a manifestation, an external translation. To kneel before God is not something that "is not very modern"; on the contrary, it corresponds to the truth of our being itself.
"One who learns to believe, also learns to kneel, and a faith and a liturgy that no longer knows about kneeling would be unhealthy in a central point. Where this gesture has been lost, we must learn it again, to remain with our prayer in the communion of the Apostles and martyrs, in the communion of the whole cosmos, in the unity with Jesus Christ himself" (J. Ratzinger, Theology of the Liturgy [Opera Omnia 11]. LEV, Vatican City 2010, p. 183).