Davidic authorship of Tehillim

The baraita now considers the authors of the biblical books: And who wrote the books of the Bible? Moses wrote his own book, i.e., the Torah, and the portion of Balaam in the Torah, and the book of Job. Joshua wrote his own book and eight verses in the Torah, which describe the death of Moses. Samuel wrote his own book, the book of Judges, and the book of Ruth. David wrote the book of Psalms by means of ten elders of previous generations, assembling a collection that included compositions of others along with his own. He included psalms authored by Adam the first man, by Melchizedek king of Salem, and by Abraham, and by Moses, and by Heman, and by Jeduthun, and by Asaph.

It is further stated that David wrote the book of Psalms by means of ten elders, whom the baraita proceeds to list. The Gemara asks: But then let it also count Ethan the Ezrahite among the contributors to the book of Psalms, as it is he who is credited with Psalms, chapter 89. Rav says: Ethan the Ezrahite is the same person as Abraham. Proof for this is the fact that it is written here: “A Maskil of Ethan the Ezrahite” (Psalms 89:1), and it is written there: “Who raised up one from the east [mizraḥ], whom righteousness met wherever he set his foot” (Isaiah 41:2). The latter verse is understood as referring to Abraham, who came from the east, and for that reason he is called Ethan the Ezrahite in the former verse.

The Gemara asks: The baraita counts Moses among the ten elders whose works are included in the book of Psalms, and it also counts Heman. But doesn’t Rav say: The Heman mentioned in the Bible (I Kings 5:11) is the same person as Moses? This is proven by the fact that it is written here: “Heman” (Psalms 88:1), which is Aramaic for trusted, and it is written there about Moses: “For he is the trusted one in all My house” (Numbers 12:7). The Gemara answers: There were two Hemans, one of whom was Moses, and the other a Temple singer from among the descendants of Samuel.

AND THOU SHALT REMEMBER THE ETERNAL THY G-D, FOR IT IS HE WHO GIVETH THEE POWER TO GET WEALTH. It is known that Israelites are mighty men, valiant men for the war because they were likened to lions and to a ravenous wolf, and they vanquished the Canaanite kings in battle. Therefore he said, “If you should think, ‘my power and the might of my hand hath gotten me this wealth,’ you should remember G-d Who brought you forth from Egypt where you had no power or might of hand at all. You should further remember that He provided all your needs for you in the wilderness, where you had nought in the power of thy hand to survive. If so [concerning] this wealth which you have won by your strength as well, [you should bear in mind that] it is G-d Who gave you the power [that was necessary for you] to accumulate the wealth; and if you forget G-d He will consume thy flesh and thy body and you will perish, just as [the nations before you] perished, for all that forsake the Eternal shall be consumed.
And then Moses reverted to bring yet another proof that you should not think ‘my power and the might of my hand etc.,’ and he said Hear, O Israel a true word from my mouth, that these nations are greater and mightier than thyself, and how will you vanquish them in battle? Besides, they have cities great and fortified up to the high heavens, and how will you capture them? Moreover, there is a people great and tall, the sons of the Anakim, whom thou knowest from the spies who saw them, and of whom thou hast heard from days of yore that no man can stand up against them. And when all this becomes clear to you, you should realize and believe from this day on that you will be unable to go over [the Jordan to do battle] before them at all until you know in your heart that the Eternal thy G-d is He Who goeth over before thee as a devouring fire, and He will destroy them, and He will bring them down. It is not the power and the might of hand He gave you, but the hand of G-d that did this to the mighty ones among them. This is an allusion to what is stated, and the Eternal cast down great stones from heaven upon them, and similarly it is said there, And there was no day like that before it or after it, that the Eternal hearkened unto the voice of a man; for the Eternal fought for Israel. The reference to the fortified cities he mentioned here is an allusion to the wall of Jericho that fell before the ark. This is what David said*, For not by their own sword did they get the Land in possession, neither did their own arm save them; but Thy right hand, and Thine arm, and the light of Thy countenance, because Thou wast favorable unto them — the right hand of G-d and His [left] arm fought against their mighty ones, and the light of His countenance that was favorable unto them [the Israelites] gave them power over those who were slain in battle. Scripture refers to this in saying further, And I destroyed the Amorite before them, whose height was like the height of the cedars, and he was strong as the oaks; yet I destroyed his fruit from above, and his roots from beneath. He [the prophet Amos] singled out the Amorite because it was the mightiest [nation] among them, and it was G-d Who destroyed it.

*Psalms 44:4. This psalm is ascribed to the sons of Korach (Verse 1). However, according to the Talmud (Baba Bathra 14b) it is David who wrote the Psalms, including among them the work of the elders, such as the sons of Korach, etc. Hence Ramban correctly writes of this psalm “that David said.” (Charles B Chavel. Shilo Pub. House. 1971-1976)