The General Instruction of the Roman Missal (GIRM) #61 states: After the First Reading follows the Responsorial Psalm, which is an integral part of the Liturgy of the Word and which has great liturgical and pastoral importance, since it fosters meditation on the Word of God.
The Responsorial Psalm should correspond to each reading and should usually be taken from the Lectionary. It is preferable for the Responsorial Psalm to be sung, at least as far as the people’s response is concerned. Hence the psalmist, or cantor of the Psalm, sings the Psalm verses at the ambo or another suitable place, while the whole congregation sits and listens, normally taking part by means of the response, except when the Psalm is sung straight through, that is, without a response. However, in order that the people may be able to sing the Psalm response more easily, texts of some responses and Psalms have been chosen for the different times of the year or for the different categories of Saints. These may be used instead of the text corresponding to the reading whenever the Psalm is sung. If the Psalm cannot be sung, then it should be recited in a way that is particularly suited to fostering meditation on the Word of God.
The adjective responsorial is defined by the Oxford diction-ary as: (of a psalm or liturgical chant) recited in parts with a congregational response between each part. As a practice here at St. Lawrence Martyr, after the psalmist intones the response or refrain, the assembly responds back with the response or refrain, hopefully without the psalmist singing with the assembly. The assembly is responsible for singing the response or refrain, while the psalmist sings the verses. This is the process of responsorial. It can be likened to Person A asking Person B “How are you?” and Person B answers “I’m fine.” Person A doesn’t answer his/her own question to Person B:
Psalmist: The Lord is my light and my salvation.
Assembly: The Lord is my light and my salvation.
Psalmist: The Lord is my light and my salvation, whom should I fear? The Lord is my life’s refuge of whom should I be afraid?
Assembly: The Lord is my light and my salvation.
Psalmist: Hear, O Lord, the sound of my call; have pity on me, and answer me. Of you my heart speaks; you my glance seeks.