Translated by Ch. Browne and J. Swallow.
S. Basil died January 1, a.d. 379. A serious illness, in addition to other causes, prevented S. Gregory from being present at his funeral (Epist. 79). Benoit holds that an expression (Epitaph, cxix. 38) in which S. Gregory says that his "lips are fettered" proves that he was still in retirement at Seleucia. This is an unwarranted deduction. In this Oration, S: 2, the Saint, alluding to his illness in disparaging terms, alleges his labours at Constantinople as a more pressing reason for his absence: and says that he undertook the task according to the judgment of S. Basil. This implies that S. Gregory went to Constantinople before the death of S. Basil, or that he had then been influenced by his friend's advice and was on the point of setting out—more probably the former, as we may be sure that, if S. Gregory had been still at Seleucia, no reason but physical incapacity would have kept him from his friend's side. His pressing duties at Constantinople and the difficulties of the long journey were the "other causes" of his letter to S. Gregory of Nyssa: and we know that he suffered from serious illness at Constantinople (Carm. xi. 887. Orat. xxiii. 1). S. Gregory left Constantinople in June, a.d. 381, and Tillemont places the date of this Oration soon after his return to Nazianzus. Benoit thinks that it was probably delivered on the anniversary of S. Basil's death. The Oration, as all critics are agreed, is one of great power and beauty. Its length (62 pages folio), the physical weakness of the speaker, and the limits of the endurance of even an interested audience, incline us to suppose that it was not spoken in its present form. We cannot well set aside expressions which clearly point to actual delivery, but it may have been amplified later.
1. It has then been ordained that the great Basil, who used so constantly to furnish me with subjects for my discourses, of which he was quite as proud as any other man of his own, should himself now furnish me with the grandest subject which has ever fallen to the lot of an orator. For I think that if anyone desired, in making trial of his powers of eloquence, to test them by the standard of that one of all his subjects which he preferred (as painters do with epoch-making pictures), he would choose that which stood first of all others, but would set aside this as beyond the powers of human eloquence. So great a task is the praise of such a man, not only to me, who have long ago laid aside all thought of emulation, but even to those who live for eloquence, and whose sole object is the gaining of glory by subjects like this. Such is my opinion, and, as I persuade myself, with perfect justice. But I know not what subject I can treat with eloquence, if not this; or what greater favour I can do to myself, to the admirers of virtue, or to eloquence itself, than express our admiration for this man. To me it is the discharge of a most sacred debt. And our speech is a debt beyond all others due to those who have been gifted, in particular, with powers of speech. To the admirers of virtue a discourse is at once a pleasure and an incentive to virtue. For when  I have learned the praises of men, I have a distinct idea of their progress: now, there is none of us all, within whose power it is not to attain to any point whatsoever in that progress. As for eloquence itself, in either case, all must go well with it. For, if the discourse be almost worthy of its subject—eloquence will have given an exhibition of its power: if it fall far short of it, as must be the case when the praises of Basil are being set forth, by an actual demonstration of its incapacity, it will have declared the superiority of the excellences of its subject to all expression in words.
 For when, etc. This seems to be the sense of an admittedly difficult sentence.
Reference address : https://www.elpenor.org/gregory-nazianzen/funeral-basil.asp