To the chief Musician upon Shoshannim, for the sons of Korah, Maschil, A Song of loves. My heart is inditing a good matter: I speak of the things which I have made touching the king: my tongue is the pen of a ready writer. My heart is inditing a good matter - רחש rachash, boileth or bubbleth up, as in the margin. It is a metaphor taken from a fountain that sends up its waters from the earth in this way. The Vulgate has eructavit, which is most literally translated by the old Psalter: Mi hert ryfted gude word. My heart belcheth - Anglo-Saxon.
I speak of the things which I have made touching the king - אמר אני מעשי למלך, literally, "I dedicate my work unto the king." Or, as the Psalter, I say my werkes til the kyng. This was the general custom of the Asiatic poets. They repeated their works before princes and honorable men; and especially those parts in which there was either a direct or constructive compliment to the great man. Virgil is reported to have a part of his Aeneid before Augustus, who was so pleased with it that he ordered ten sestertia to be given him for every line. And the famous Persian poet Ferdusi read a part of his Shah Nameh before Sultan Mahmoud, who promised him thirty thousand denars for the poem.
My tongue is the pen of a ready writer - I shall compose and speak as fluently the Divine matter which is now in my heart, as the most expert scribe can write from my recitation. My tung of maister swiftly wrytand. "That es, my tung is pen of the Haly Gast; and nout but als his instrument, wham he ledis als he wil. For I speke noght bot that he settis on my tung; als the pen dos noght withouten the writer. Swyftly wrytand, for the vertu of goddes inspiracioun is noght for to thynk with mons study, that he schewes til other of the purete of heven; that es some for to com that he wrytes." - Old Psalter.