This is the most succinct I have found Agamben on Paul and the Law. (He wrote a whole book on it, The Time That Remains, but besides that he brings it up often). The second paragraph is what matters here, the rest are given for context, the italics are original but boldface is my emphasis.
The considerations developed up to now must have rendered obvious the sense in which it is almost impossible to pose the problem of the juridical or nonjuridical nature of the monastic rules without falling into anachronism. Even granting that something like our term juridical has always existed (which is no less dubious), it is certain, in any case, that it means one thing in Roman law, another in the early centuries of Christianity, another still starting from the Carolingian age, and another, finally, in the modern age, when the State begins to assume the monopoly over law. Furthermore, the debates that we have analyzed over the “legal” or “advisory” character of the rules, which seem to approach the terms of our problem, become intelligible only if one does not forget that they are superimposed over the theological problem of the relation between the two diathēkai, the Mosaic law and the New Testament.
In this sense, the problem ceases to be anachronistic only if it is restored to its proper theological context, which is that of the relationship between evangelium and lex (that is, first of all, the Hebraic law). The theory of this relationship was elaborated in the Pauline letters and culminates in the declaration that Christ as messiah is telos nomou, end and fulfillment of the law (Rom. 10:4). Even if in the same letter this radical messianic thesis —and the opposition that it implies between pistis and nomos—is complicated to the point of giving rise to a series of aporias (as in 3:31: “Do we then render the law inoperative by this faith? By no means! On the contrary , we uphold the law”), it is nonetheless certain that the Christian life is no longer “under the law” and cannot in any case be conceived in juridical terms. The Christian, like Paul, is “dead to the law” (nomōi apethanon; Gal. 2:19), and lives in the freedom of the spirit. Even when the Gospel is counterposed to the Mosaic law as a “law of faith” (Rom. 3:27), or later as a nova lex to the vetus, it remains the case that neither its form nor its content are homogeneous to those of the nomos. “The difference between the law and the Gospel,” one reads in Isidore’s Liber differentiarum (chap. 31), “is this: in the law there is the letter, in the Gospel grace . . . the first was given for transgression, the second for justification; the law shows sin to the one who does not know it, grace helps him to avoid it . . . in the law the commandments are observed, in the fullness of the Gospel the promises are consummated.”
It is in this theological context that one must situate the monastic rules. Basil and Pachomius, to whom we owe, so to speak, the archetypes of the rules, are perfectly conscious of the irreducibility of the Christian form of life to the law. Basil, in his treatise on baptism, explicitly confirms the Pauline principle according to which the Christian dies to the law (apothanein tōi nomōi), and as we have seen, Pachomius’s Praecepta atque iudicia opens with the statement that love is the fulfillment of the law (plenitudo legis caritas). The rule, whose model is the Gospel, cannot therefore have the form of law, and it is probable that the very choice of the term regula implied an opposition to the sphere of the legal commandment. It is in this sense that a passage from Tertullian seems to oppose the term rule to the “form of the [Mosaic] law”: “Once the form of the old law was dissolved [veteris legis forma soluta], this is the first rule which the apostles, on the authority of the Holy Spirit, sent out to those who were already beginning to be gathered to their side out of the nations” (Tertullian 3, 12). The nova lex cannot have the form of law, but as regula, it approaches the very form of life, which it guides and orients (regula dicta quod recte ducit, recalls an etymology from Isidore, Etymologiarum 6.16).
The problem of the juridical nature of the monastic rules here finds both its specific context and its proper limits. Certainly the Church will progressively construct a system of norms that will culminate in the twelfth century in the system of canon law that Gratian compiles in his Decretum. But if Christian life doubtless can readily encounter the sphere of law, it is just as certain that the Christian forma vivendi itself—which is what the rule has in view—cannot be exhausted in the observance of a precept, which is to say that it cannot have a legal nature.
Agamben, The Highest Poverty: Monastic Rules and Form-of-Life, 45-47.