But, one might ask, is this perennial teaching doctrinal (could be divinely revealed, or is at least consistent with apostolic teaching and practice, yet possibly subject to revision), or dogmatic (divinely revealed in Scripture and Tradition, defined as clearly as possible/necessary with full authority, and not subject to revision as far as the definition goes)?
Doctrine and dogma are not opposed to each other, in the sense that the first is optional and the second not. Both are to be received as fully as humanly possible, for living and believing with "the mind of Christ," and for not living "according to this age" (Rom 12:2, etc). There's no difference of truth between them, but there is a difference of clarity and of finality. Dogmatic teaching is the highest level of exercising the teaching authority of the Church (Magisterium); doctrinal teaching is the ordinary level of the same.
To asnwer the question posed, consider a small sample of points:
- The quote in the first paragraph, above, shows without ambiguity that the indissolubility of marriage is taught by Christ Himself, directly.
- The 24th session of the Council of Trent (Nov, 1563) dealt with marriage, and its decrees and canons were accepted and promulgated by Pope Pius IV. It certainly appears to be a formal, solemn, and intended-to-be-dogmatic definition of marriage, including its indissolubility.
- Pope Pius XI, in the encyclical Casti Connubi (1930), refers to that definition of Trent as a "solemn definition," and repeats the unchanging teaching of indissolubility with great clarity.
- The Second Vatican Council, in its sacred consititution Gaudium et Spes, repeats the same (e.g. #48, albeit without the same verbal markers of dogmatic intent; it does, however, cite Casti Connubi, which seems to imply dogmatic intent, given that document's clarity).
- The Catechism of the Catholic Church repeats the same again (e.g. #1639, 1640, etc), without ambiguity. It cites the same biblical passage above, and GS #48.
Moreover, all these sources consistently present a clear and compelling theological reason why marriage ought to be indissoluble; namely, that God, in establishing the natural of marriage, does so on the pattern of the divine covenant. This is a thoroughly Scriptural and Traditional claim (e.g., Jer 31:31, Dan 2:44, Eph 5, etc.). Since God's covenant is indissoluble, marriage must also be. To claim that marriage is soluble is to claim that the divine covenant is also soluble, that God could change His mind about the promises of salvation; or in other words, that Christ died, but not for our sins (!). If marriage has any spiritual reality at all, it must, then, necessarily be indissoluble.
Given all this sort of evidence, it seems to me very difficult to claim that the indissolubility of marriage is merely a doctrinal, but not a dogmatic, teaching.