So I swear by whatsoever you see, and by whatsoever you see not, that this is verily the word of an honored Messenger.
meaning, Muhammad. Allah gave this description to him, a description which carries the meaning of conveying, because the duty of a messenger is to convey from the sender. Therefore, Allah gave this description to the angelic Messenger in Surah At-Takwir, where he said,
إِنَّهُ لَقَوْلُ رَسُولٍ كَرِيمٍ ذِى قُوَّةٍ عِندَ ذِى الْعَرْشِ مَكِينٍ مُّطَـعٍ ثَمَّ أَمِينٍ
Verily, this is the Word of (this Qur'an brought by) a most honorable messenger. Owner of power (and high rank) with Allah, the Lord of the Throne. Obeyed and trustworthy. (81;19-21)
And here, it refers to Jibril.
Then Allah says,
وَمَا صَـحِبُكُمْ بِمَجْنُونٍ
and your companion is not a madman. (81;22)
meaning, Muhammad .
وَلَقَدْ رَءَاهُ بِالاٍّفُقِ الْمُبِينِ
And indeed he saw him in the clear horizon. (81;23)
meaning, Muhammad saw Jibril in his true form in which Allah created him.
وَمَا هُوَ عَلَى الْغَيْبِ بِضَنِينٍ
And he is not Danin with the Unseen. (81;24)
meaning, suspicious.
وَمَا هُوَ بِقَوْلِ شَيْطَـنٍ رَّجِيمٍ
And it (the Qur'an) is not he word of the outcast Shaytan. (81;25)
This is similar to what is being said here.
وَمَا هُوَ بِقَوْلِ شَاعِرٍ قَلِيلً مَا تُوْمِنُونَ