I am repeating the post above, but with the final text of the translation of the Roman Missal, as approved for Australia.
I think the Roman Missal says to stand for the Sequence. From the General Instruction of the Roman Missal (GIRM):
The Acclamation before the Gospel **
62. After the reading that immediately precedes the Gospel, the Alleluia or another chant laid down by the rubrics is sung, as the liturgical time requires. An acclamation of this kind constitutes a rite or act in itself, by which the gathering of the faithful welcomes and greets the Lord who is about to speak to them in the Gospel and profess their faith by means of the chant. It is sung by everybody, standing, and is led by the choir or a cantor, being repeated as the case requires. The verse, on the other hand, is sung either by the choir or by a cantor.
a. The Alleluia is sung in every time of the year other than Lent. The verses are taken from the Lectionary or the Graduale.
b. During Lent, in place of the Alleluia, the Verse before the Gospel as given in the Lectionary is sung. It is also permissible to sing another Psalm or Tract, as found in the Graduale.
63. When there is only one reading before the Gospel:
a. during a season when the Alleluia is prescribed, either an Alleluia Psalm or the Responsorial Psalm followed by the Alleluia with its verse may be used;
b. during a time of the year when the Alleluia is not foreseen, either the Psalm and the Verse before the Gospel or the Psalm alone may be used;
c. the Alleluia or the Verse before the Gospel, if not sung, may be omitted.
64. The Sequence which, except on Easter Sunday and on Pentecost Day, is optional, is sung before the Alleluia.
**
The Homily
Arguments to stand for the Sequence are as follows:
- Paragraph 64 about the Sequence is listed under the heading “The Acclamation before the Gospel”. Therefore the instruction to stand in n. 62 should be considered to apply to it: “It is sung by everybody, standing, and is led by the choir or a cantor, being repeated as the case requires.”
- The description of the thing to be stood for includes “After the reading that immediately precedes the Gospel”. Clearly the Sequence is after the reading that immediately precedes the Gospel.
- In GIRM n. 43 it lists the times to sit. The Sequence is not listed. “The faithful should sit, on the other hand, during the readings before the Gospel and the Responsorial Psalm and for the Homily and during the Preparation of the Gifts at the Offertory; and, if appropriate, during the period of sacred silence after Communion.”
An argument to sit for the Sequence is:
GIRM n. 43 lists the times to stand. The Sequence is not listed. It has “43. The faithful should stand from the beginning of the Entrance Chant, or while the priest approaches the altar, until the end of the Collect; for the Alleluia Chant before the Gospel; …”. The Sequence is not the Alleluia chant, so there is no instruction to stand for it.
But a counter argument to this is that there is no Alleluia chant during Lent. There is a verse before the Gospel with something like “Praise to you, Lord Jesus Christ …”. People would stand for that.