He was a king. Why does he say he is poor, and call himself devoted?
Two lines near the start sound odd from a king. First: "I am poor and needy" (verse 1). Then: "I am a chasid" (verse 2), which means devoted and kind. Isn't that bragging?
On the first line, Radak says David wrote this while running from King Shaul, and he really was poor then. He could not support himself unless relatives and men of his tribe helped him in secret. Ibn Ezra (a Spanish commentator who died in the 1160s) gives other options: poor in his own eyes, or poor next to the kings of the nations.
On the second line, Radak admits some people are puzzled. His answer is that David's heart was honest. Even when he sometimes sinned, he regretted it. And he spoke of himself as a chasid only in comparison to his enemies, who did him harm while he did them none. He even saved Shaul more than once.
The Gemara (the record of the rabbis' debates, finished about 1,500 years ago) explains this verse in Berakhot 4a. Two rabbis give two answers. In one, David says: the kings of the east and west sleep late, while I get up at midnight to thank You. In the other: all those kings sit in their honor, while my hands are dirty with blood and afterbirth, ruling that a woman is pure for her husband. And whatever he did, he checked with his teacher Mefiboshet and was not embarrassed to ask.
Then the Gemara asks how David could call himself a chasid at all. In Tehillim 27:13 there are dots over the word lulei, "had I not," which the Gemara reads as doubt: he trusted God to reward the righteous but was not sure he was one of them. It answers that David was afraid a sin might spoil it.
Midrash Tehillim adds that chasid is God's own title, from Yirmeyahu (the prophet Jeremiah) 3:12. It says David kept silent when people cursed him, the way God stays silent when the nations insult Him.
Radak on Tehillim 86:1 and 86:2,Ibn Ezra on Tehillim 86:1,Berakhot 4a,Midrash Tehillim 86:1; Yirmeyahu 3:12"Make my heart one"? I only have one heart. What is David asking for?
Verse 11 says, "Teach me Your way, Hashem, I will walk in Your truth; make my heart one to fear Your name." The Hebrew word is yached, from the word for "one" or "together." Ibn Ezra says it comes either from yachid, "one," or from joining. So David asks God to make his heart one. Most of us know the feeling of wanting two things at once.
Radak reads it as a worry about where attention and fear go. He says David already knew by tradition that God alone is God. Still, he asks to learn more about how God made the world. Then he asks that his heart not "turn this way and that," but be united to fear God's name, so he fears no person, only God.
The next verse says the same from the other side. When God unites his heart, David will thank Him "with all my heart." Radak explains that no part of his heart or thoughts will be aimed at anyone else.
Midrash Tehillim hears a different problem. It reads "with all my heart" as "with the good inclination and the bad one, so that there is no crookedness in them." The Mishnah (the earliest book of rabbinic law, from about 1,800 years ago) reads "with all your heart" in the Shema the same way, as both inclinations (Berakhot 9:5). On that reading, the goal is not for one of the pulls to vanish. It is for both of them to be straight, and both to serve God.
Abudarham says the Ahavat Olam line, "make our hearts one to love and to fear Your name," is built on this verse. The Ahavat Olam page tells more.
Tehillim 86:11-12,Ibn Ezra and Radak on Tehillim 86:11-12,Midrash Tehillim 86:5,Mishnah Berakhot 9:5,Abudarham, Blessings on the Shema 10What is the "sign for good" David asks for at the end?
The last verse asks: "Give me a sign for good, so those who hate me will see it and be ashamed." A sign of what? The sources do not agree.
Radak says the sign is the kingship itself. It will show David's enemies that God chose him long ago.
Midrash Tehillim finds the sign in David's own life. The sign for good is about Ahitophel, the adviser who turned against him. "You helped me" is about Chushai the Archite, whose advice Avshalom's people chose over Ahitophel's. "And comforted me" is about the prophet Natan, who told David, "Hashem has also removed your sin" (Shmuel II 12:13).
The Gemara tells it another way (Shabbat 30a, Sanhedrin 107b). David asked God to forgive him for that sin. The discussion in Sanhedrin 107a takes it to be the matter of Bat Sheva and Uriah, since God answers him with the verse about a man who sleeps with his neighbor's wife. God said it was forgiven. David then asked for a sign in his lifetime, so everyone would know. God answered that in David's lifetime He would not make it known, but in his son Shlomo's lifetime He would.
Shabbat 30a says how. When Shlomo built the Temple, the gates stuck together as he tried to bring in the Ark. They opened only when he said, "Remember the kindnesses of David Your servant." Then the faces of David's enemies turned dark "like the bottom of a pot," and everyone knew God had forgiven David.
Not every teacher tells David's story the same way. In Shabbat 56a, Rabbi Shmuel bar Nachmani says in Rabbi Yonatan's name that anyone who says David sinned is mistaken. The same passage still finds fault with him: he should have put Uriah on trial instead of having him killed in battle.
Tehillim 86:17,Radak on Tehillim 86:17,Midrash Tehillim 86:7,Shabbat 30a; Sanhedrin 107b,Shabbat 56a