The judgment
豫：利建侯行師。
Enthusiasm. It is favorable to install leaders and to move the army: joy that has direction can organize people.
Received text; plain English after the Chinese. Source: 周易經傳 (public-domain). Passage: hex16.judgment.
The image
象曰：雷出地奮，豫。先王以作樂崇德，殷薦之上帝，以配祖考。
Thunder comes out of the earth: enthusiasm. The old kings made music, honored virtue, and offered it up to heaven with their ancestors.
Received text; plain English after the Chinese. Source: 周易經傳 (public-domain). Passage: hex16.image.
Joy moves people; without a center it becomes noise.
The six lines
Each line is a stage, from the bottom of the hexagram to the top. Open any line to read it in plain English.
初六 鳴豫，凶。 Announcing your joy too loudly. Misfortune: the celebration outruns the substance.
Announcing your joy too loudly. Misfortune: the celebration outruns the substance.
六二 介於石，不終日，貞吉。 Firm as a stone, and it does not last the day. Stay true and it is lucky: you see through the excitement quickly.
Firm as a stone, and it does not last the day. Stay true and it is lucky: you see through the excitement quickly.
六三 盱豫，悔。 遲有悔。 Looking around for approval, and it brings regret. Delay also brings regret: flattery is a trap either way.
Looking around for approval, and it brings regret. Delay also brings regret: flattery is a trap either way.
九四 由豫，大有得。勿疑。 朋盍簪。 Joy has a source, and great gain comes. Do not doubt; friends gather like hair in a clasp.
Joy has a source, and great gain comes. Do not doubt; friends gather like hair in a clasp.
六五 貞疾，恆不死。 A chronic condition, but it does not kill. Stay steady: some heaviness is simply long.
A chronic condition, but it does not kill. Stay steady: some heaviness is simply long.
上六 冥豫，成有渝，無咎。 Joy in the dark, then a change when it is complete. No blame: even late, you can wake up.
Joy in the dark, then a change when it is complete. No blame: even late, you can wake up.