You can read up on what Cardinal William Levada, the last CDF head, had to say about graviora delicta (grave crimes).
RS 172 treats with matters largely that only priests can do The footnotes are rather large, so I left them grouped at the bottom of RS 172:
1. Graviora delicta
[172.] Graviora delicta against the sanctity of the Most August Sacrifice and Sacrament of the Eucharist are to be handled in accordance with the ‘Norms concerning graviora delicta reserved to the Congregation for the Doctrine of the Faith’,[280] namely:
a) taking away or retaining the consecrated species for sacrilegious ends, or the throwing them away;[281]
b) the attempted celebration of the liturgical action of the Eucharistic Sacrifice or the simulation of the same;[282]
c) the forbidden concelebration of the Eucharistic Sacrifice with ministers of Ecclesial Communities that do not have the apostolic succession nor acknowledge the sacramental dignity of priestly Ordination;[283]
d) the consecration for sacrilegious ends of one matter without the other in the celebration of the Eucharist or even of both outside the celebration of the Eucharist.[284]
[280] Cf. Pope John Paul II, Apostolic Letter (Motu Proprio), Sacramentorum sanctitatis tutela: AAS 93 (2001) pp. 737-739; Congregation for the Doctrine of the Faith, Ep. ad totius Catholicae Ecclesiae Episcopos aliosque Ordinarios et Hierarchas quorum interest: de delictis gravioribus eidem Congregationi pro Doctrina Fidei reservatis: AAS 93 (2001) p. 786.
[281] Cf. Code of Canon Law 1367; Pontifical Council for the Interpretation of Legislative Texts, Responsio ad propositum dubium, 3 July 1999: AAS 91 (1999) p. 918; Congregation for the Doctrine of the Faith, Ep. ad totius Catholicae Ecclesiae Episcopos aliosque Ordinarios et Hierarchas quorum interest: de delictis gravioribus eidem Congregationi pro Doctrina Fidei reservatis: AAS 93 (2001) p. 786.
[282] Cf. Code of Canon Law 1378 § 2. 1 & 1379; Congregation for the Doctrine of the Faith, Ep. ad totius Catholicae Ecclesiae Episcopos aliosque Ordinarios et Hierarchas quorum interest: de delictis gravioribus eidem Congregationi pro Doctrina Fidei reservatis: AAS 93 (2001) p. 786.
[283] Cf. Code of Canon Law 908 & 1365; Congregation for the Doctrine of the Faith, Ep. ad totius Catholicae Ecclesiae Episcopos aliosque Ordinarios et Hierarchas quorum interest: de delictis gravioribus eidem Congregationi pro Doctrina Fidei reservatis: AAS 93 (2001) p. 786.
[284] Cf. Code of Canon Law 927; Congregation for the Doctrine of the Faith, Ep. ad totius Catholicae Ecclesiae Episcopos aliosque Ordinarios et Hierarchas quorum interest: de delictis gravioribus eidem Congregationi pro Doctrina Fidei reservatis: AAS 93 (2001) p. 786.
These four all impact the connection between faith of the laity and the sacraments and how they are conducted.
2. Grave Matters
[173.] Although the gravity of a matter is to be judged in accordance with the common teaching of the Church and the norms established by her, objectively to be considered among grave matters is anything that puts at risk the validity and dignity of the Most Holy Eucharist: namely, anything that contravenes what is set out above in nn. 48-52, 56, 76-77, 79, 91-92, 94, 96, 101-102, 104, 106, 109, 111, 115, 117, 126, 131-133, 138, 153 and 168. Moreover, attention should be given to the other prescriptions of the Code of Canon Law, and especially what is laid down by canons 1364, 1369, 1373, 1376, 1380, 1384, 1385, 1386, and 1398.
I leave it for those more versed and interested in canon law to add more commentary.
Catholic Sensibility 