Commenting on the topic of intercession and the placating of God’s anger against sins, Staníslaus Lyonnet wrote the following:
Expiation and Intercession
In those rare passages where the two terms “expiation” and “anger” are found together, we notice that it is in association with prayer. This is true in the expiation of Moses (Ex 32:30; cf. 32:11), and in the case of Aaron (Nm 17:11ff.) according to the interpretation of Wis 18:21-25; see that of Phineas according to the Targum (cf. Ps 106:30); and it is especially clear in the case of the Servant of Yahweh whose role as intercessor is mentioned four times (Targum Is 5:4, 7, 11, 12). St. Jerome had this notion of expiation in mind when (following the usage of the old Latin versions) he translated the stereotyped phrase which concludes the description of the sacrifices for sin, “to make atonement for them,” (Lv 4:20, 26, 31, etc.) by a verb which had the meaning “to pray” or “to intercede.”
It is not surprising, then, to find in the Epistle to the Hebrews the essential function of the priestly activity of Christ as he enters into heaven described in terms of “intercession” (Heb 7:25; 9:24). He is seen as the High Priest who has gone beyond the veil to perform the sacrificial rite par excellence, the sprinkling of his blood on the propitiatory.
This underscores the importance of the interior dispositions of the one who is making the expiation. The external gesture is only the expression of the internal spiritual act, and it is no substitute for it. It is also evident that man’s expiatory acts are not some kind of an attempt to force God to be propitious. When Wisdom describes the intercession of Aaron, it is careful to note that his prayer consists in recalling to God the oaths and agreements given to the forefathers (Wis 18:22). Such a prayer is basically an act of faith in the faithful love of Yahweh. Seen in this way, expiation has for its purpose not to change the dispositions of God (except as man sees it), but to dispose man to receive the gift of God. (Staníslaus Lyonnet, “Expiation,” in The Theology of the Atonement: Readings in Soteriology, ed. John R. Sheets [Englewood Cliffs, N.J.: Prentice-Hall, Inc., 1967], 99-101, here, pp. 100-1)
While it is hard to find as it is unfortunately out of print, one should try to get Lyonnet’s book on the atonement and related topics:
Sin, Redemption, and Sacrifice: A Biblical and Patristic Study (Analecta Biblica 48; Rome: Biblical Institute Press, 1970)
On Moses' intercession in Exo 32-33 and other similar events, as well as their theological implications, see my lengthy critique of Reformed theology: