The gap between our words and God's Word
Augustine is contrasting human spoken words, which we make from bodily matter, with God the Father's begetting of the Word, which is from his very self.
But between our mind and our words, by which we try to show the mind itself, there is a very great distance. We do not beget sounding words; we make them. And for making them, the body lies beneath as matter. Yet there is a very great difference between mind and body. God, however, when he begot the Word, begot what he himself is—not from nothing, and not from some already made and created matter, but from himself, what he himself is. This is what we too are attempting when we speak, if we carefully consider the impulse of our will—not when we lie, but when we speak the truth. What else are we trying to do except to bring our very mind, if it can be done, into the mind of the hearer to be known and seen? So that we ourselves remain in ourselves and do not withdraw from ourselves, and yet we bring forth a sign by which knowledge of us comes to be in another—so that, as far as our ability allows, a kind of second mind is brought forth from the mind, through which it makes itself known. We do this by trying with words and with the very sound of the voice and with facial expression and bodily gesture—with all these devices, desiring to show what is within, because we cannot bring forth such a thing itself. And therefore the mind of the speaker cannot become fully known. This is also why there is room for lies. But God the Father, who both willed and was able to make himself known most truly to minds that would know him, begot for the purpose of making himself known that which he himself is who begot—who is also called his power and wisdom, because through him he worked and ordered all things. Of him it is said for this reason: "She reaches from end to end mightily, and she orders all things sweetly" (Wisdom of Solomon 8:1).
Latin
Inter animum autem nostrum et uerba nostra, quibus eundem animum ostendere conamur, plurimum distat. nos quippe non gignimus sonantia uerba, sed facimus: quibus faciendis materia subiacet corpus. plurimum autem interest inter animum et corpus. deus uero, cum uerbum genuit, id quod est ipse genuit, neque de nihilo neque de aliqua iam facta conditaque materia, sed de se ipso id quod est ipse. hoc enim et nos conamur, cum loquimur, si diligenter consideremus nostrae uoluntatis adpetitum, non cum mentimur, sed cum uerum loquimur. quid enim aliud molimur, nisi animum ipsum nostrum, si fieri potest, cognoscendum et perspiciendum animo auditoris inferre? ut in nobis quidem ipsi maneamus nec recedamus a nobis et tamen tale indicium, quo fiat in altero nostra notitia, proferamus, ut, quantum facultas conceditur, quasi alter animus ab animo, per quem se indicet, proferatur. id facimus conantes et uerbis et ipso sono uocis et uultu et gestu corporis, tot scilicet machinamentis id, quod intus est, demonstrare cupientes, quia tale aliquid proferre non possumus; et ideo non potest loquentis animus penitus innotescere. unde etiam mendaciis locus patet. deus autem pater, qui uerissime se indicare animis cognituris et uoluit et potuit, hoc ad se ipsum indicandum genuit, quod est ipse qui genuit: qui uirtus etiam eius et sapientia dicitur, quia per ipsum operatus est et disposuit omnia. de quo propterea dicitur: adtingit a fine usque ad finem fortiter, et disponit omnia suauiter.