"The obedience of the star calls us to imitate its humble service: to be servants, as best we can, of the grace that invites all men to find Christ."

Trier, Stadtbibliothek 24
(Codex Egberti), 17r.

     Leo the Great, Sermo 33 =3 in Epiphania Domini, Recension A (6 January 443), as translated at Liturgy of the hours 1, 561.  FC 93, trans. Jane P. Freeland and Agnes J. Conway, 142:

This star's subservient function incites us to imitate its submission, so that we may render service to this grace which invites all to Christ, in as much as we can. 

Cuius utique famulatus ad formam nos sui hortatur obsequii, ut huic gratiae quae omnes inuitat ad Christum, quantum possumus, seruiamus [(CCSL 138, 176-177 (170-177); PL 54, col. 244)].

     Earlier in this same sermon, Leo reminds us that Abraham had been promised "countless descendants. . . . generated not from the seed of flesh, but from the fecundity of faith"; that "These were compared to the stars in number"; and that "In order to create this promised posterity, the heirs (symbolically represented in the stars) are [therefore fittingly] quickened by the birth of a new star, so that this new honor given by heaven might serve the one for whom the witness of heaven had been summoned" (FC 93, 139-140).  Thus,

Abraham 'saw' this day 'and rejoiced.'  He rejoiced when he realized that the children of his faith would be blessed 'in his seed, which is Christ' [(FC 93, 142, underscoring mine)].

This [then] is the day that Abraham saw, and rejoiced to see, when he knew that the sons born of his faith would be blessed in his seed, that is, in Christ [(Liturgy of the hours 1, 561, underscoring mine)].

Hunc diem Abraham vidit, et gavisus est, cum benedicendos fidei suae filios in semine suo, quod est Christus, agnovit [(PL 54, col. 243C, underscoring mine)].