Psalm 41's title says it is For the Chief Musician and is A Psalm by David. It opens with a promise for kind people: Blessed is he who considers the poor. Yahweh will deliver him in the day of evil. Yahweh will preserve him, and keep him alive. Yahweh will sustain him on his sickbed, and restore him from his bed of illness. God notices those who notice the needy.
Then David speaks of his own sickness and sin. I said, Yahweh, have mercy on me! Heal me, for I have sinned against you. His enemies speak evil against him. A visitor comes, speaks falsehood, then goes out and spreads gossip. All who hate me whisper together against me. They say an evil disease has afflicted him and he will not rise again. The deepest pain is betrayal: Yes, my own familiar friend, in whom I trusted, who ate bread with me, has lifted up his heel against me. In the New Testament, Jesus applies these words to Judas on the night he was betrayed (John 13:18).
David turns again to Yahweh for mercy and asks God to raise him up. By this I know that you delight in me, because my enemy doesn't triumph over me. As for me, you uphold me in my integrity, and set me in your presence forever. The psalm ends with a doxology that, in many Bibles, closes Book One of the Psalms: Blessed be Yahweh, the God of Israel, from everlasting and to everlasting! Amen and amen. A doxology is a short song of praise to God.