Here are the references against removal of maniple and/or chasuble.
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“Many rubricians direct the celebrant to remove his chasuble and maniple if he goes to the pulpit. There is no rubric which orders this. When the bishop preaches at pontifical Mass, he does so clad in the Mass vestments; if the assistant priest replaces him he is bidden to preach ‘sic paratus’ (i.e. in his cope, C.E. I, vii, 4). When the subdeacon goes to sing the Epistle, or the deacon the Gospel at an ambo, they are not directed to remove even the maniple. From the standpoint of the rubrics, therefore, there is no reason why the celebrant should remove his chasuble and maniple to perform an act which is part of the liturgy.”
O’Connell, J. B. [John Berthram], The Celebration of Mass: A Study of the Rubrics of the Roman Missal, Bruce Publishing: Milwaukee, 1964, p. 484, n.55.
*For a discussion of the 1964 edition of O’Connell, see Alcuin Reid, 12 February 2007: [ http://www.newliturgicalmovement.org/2007/02/guest-piece-by-dr-alcuin-reid-review-of.html ] – – – – –“If the celebrant himself preaches, he may do so at the altar at the Gospel side or he may go to the pulpit (conducted by the M.C.). He does not take off his maniple or chasuble. The ministers sit at the sedilia. At the end of the sermon, they join the celebrant when he arrives from the pulpit and go with him, in the usual (longer) way, to the altar.”
Under the heading of: “De concione infra Missam sine planeta et manipulo.” [The sermon within Mass without chasuble and maniple.]
The final word is: “sapit proinde talem hic ritus novitatem, ut reprobatione sit Dignus.”
[“therefore know that novelty in the rites such as this is worthy of rejection” or “it is wise that such ritual novelties are worthy of disapproval.”]
Centro liturgico vincenziano, Ephemerides liturgicae, Vol. 6, No. 6, Cuggiani Press: Rome, 1892, p. 288.
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The contrary opinion of Lohner in 1759 is perhaps due to the “novelty” of preaching inside of Mass, something Jesuit missionaries around the world were not accustomed to:
“If the Celebrant himself preaches, let him stay on the Gospel side; chasuble and maniple are laid aside, but if this can not conveniently be done, the chasuble and maniple are laid aside at the sedilia and he proceeds without the ministers.”
Lohner, R. P. Tobia, S.J., Instructio practica prima de Ss. Missae sacrificio juxta Ritum Romanae Ecclesiae offerendo, Bencard Press: 1759, p. 54.
Adrian Fortescue mentioned above has only a footnote in 1917 which repeats Lohner:
“If the celebrant himself preaches, he may do so at the altar, in which case he need only take off the maniple and hand it to the M.C., who lays it at the sedile [sic]. If he preaches from a pulpit, generally he will go to the sedilia with the ministers, take off the chasuble and maniple (assisted by the M.C.), and will leave them there. The M.C. may accompany him to the pulpit. The ministers sit at the sedilia. At the end of the sermon the celebrant comes to the sedilia and puts on the chasuble and maniple; the ministers go with him, in the usual (longer) way, to the altar.” (page 124, n. 1)
As late as 1956 Mueller repeats Fortescue:
“If the C[elebrant] himself preaches, he may do so either at the altar or from the pulpit; in the later case he removes the chasuble and maniple but wears the biretta (where it is customary.)
In Handbook of Ceremonies by John Baptist Mueller, SJ (revised and edited by Adam C. Ellis, SJ). St. Louis, Mo. and London: B. Herder, 1956, p. 193.
*Formerly both the distribution of Holy Communion and preaching were done outside of Mass. The practice of removing the chasuble and maniple [which are specifically eucharistic] to preach comes from when preaching was done outside of Mass, usually before the Mass. The practice may have orginated in the hotter Mediterranean climate. In an era before microphones, preaching may have been much closer to classical rhetoric when hand gestures supported the voice. The location of the pulpit in the middle of the church, well outside the sanctuary area, may have contributed to the “non eucharistic” and therefore extrinsic perception of preaching. The Fore-Mass or Liturgy of the Catechumens did not demand eucharistic vestments. Less concrete arguments seem unconvincing.
*Holy Communion was distributed after the final blessing, i.e., after Mass. The priest said “Ite missa est” and then went to the tabernacle to retrieve the ciborium and to give Holy Communion to the faithful.
*** With thanks to Father David Jenuwine of the Diocese of Saginaw, Michigan.