אָֽנָּ֣ה יְהוָה֮ כִּֽי־אֲנִ֪י עַ֫בְדֶּ֥ךָ אֲֽנִי־עַ֭בְדְּךָ בֶּן־אֲמָתֶ֑ךָ פִּ֝תַּ֗חְתָּ לְמוֹסֵרָֽי׃
여호와여 나는 진실로 주의 종이요 주의 여종의 아들 곧 주의 종이라 주께서 나의 결박을 푸셨나이다
Midrash Tanchuma
Male-servants refers to Moses, as is said: Moses was a servant of the Lord (Deut. 34:5). Maid-servants alludes to Ruth, from whom David descended, and concerning whom it is written: I am thy servant, the servant of thy maid-servant (Ps. 116:16). He was the descendant of the woman who forsook being an important lady and a queen in order to find shelter beneath the wings of the Shekhinah.2Tradition tells us that Ruth was the daughter of Eglon, the king of Moab. She would have become a queen if she had not left her native land for the land of Israel.
Ein Yaakov (Glick Edition)
Raba lectured: "What does the passage (Ps. 116, 16) Thou hadst loosened my fetters, mean? Thus said David before the Holy One, praised be He! — 'Sovereign of the Universe! Thou hast absolved two restrictions which were against me, they are Ruth the Moabite and Na'amah the Ammonite.'" Raba lectured: "What is the meaning of the passage (Ib. 40, 6) Many things hast Thou done, O Lord my God! Thy wonderful deeds and Thy thoughts toward us? It does not say toward me, but toward us. From this it may be inferred that Rehobo'am was sitting in David's lap, and the latter said that concerning you and me refer the two [above quoted] passages." Raba lectured: "What does the passage (Ib., ib., 8) Then said I: 'Lo, I come in the scroll of the book it is written down for me,' mean? David said: 'I thought that I came [to my royalty] just now by a mere incident, and I was not aware of the fact that, in the roll of the book [dating from Abraham,] it is written down concerning me; for it is written there (Gen. 19, 15) Hanimtza'oth (that are here), and here it is written (Ps. 89, 21) Matzathi (I have found), David My servant: with My holy oil," etc.
Midrash Tehillim
Another thing to the conductor, to serve God. What did David see fit to say to the servant of God? To teach you that anyone who repents for their sins, the Almighty adds honor to them and calls them a beloved name. Come and see this in the case of the sons of Korah: until they repented, they were not called beloved, but after they repented, they were called beloved (Psalms 45:1). To the conductor, on Shoshanim. When they repented, they were called friends, as it says, "To the conductor, on the Shoshanim, for the sons of Korah, a maskil, a song of friendship" (Psalms 47:1). You also find this with David, as until he repented, he was not included in the upper assembly, but after he repented, he was included in the upper assembly and was called the servant of God, to the conductor, for the servant of God. You will find that anyone who calls themselves a servant, the Almighty calls them a servant. Abraham called himself a servant (Genesis 18:3), "My lord, if now I have found favor in your sight, do not pass on by your servant." And the Almighty called him a servant (Genesis 26:24), "Because Abraham obeyed Me and kept My charge, My commandments, My statutes, and My laws." Jacob called himself a servant (Genesis 32:11), "I am not worthy of all the mercies, and of all the truth, which You have shown to Your servant." And the Almighty called him a servant (Isaiah 44:1), "But now listen, O Jacob, My servant." Moses called himself a servant (Deuteronomy 3:24), "O Lord God, You have begun to show Your servant Your greatness and Your mighty hand." And the Almighty called him a servant (Numbers 12:7), "Not so with My servant Moses." David called himself a servant (Psalms 116:16), "Truly, I am Your servant, the son of Your maidservant." And the Almighty called him a servant (2 Samuel 3:18), "By the hand of David, My servant, I will save." And there were those who did not call themselves servants, but the Almighty called them servants. Isaac did not call himself a servant, but the Almighty called him a servant (Exodus 32:13), "Remember Abraham, Isaac, and Israel, Your servants." Joshua did not call himself a servant, but he was called a servant (Joshua 24:29), "And Joshua, the son of Nun, the servant of the Lord, died.