One night in 1967, the phrase "words are flowing out like endless rain into a paper cup" came to Lennon after hearing his ex-wife Cynthia, according to Lennon, "going on and on about something." Later, after "she'd gone to sleep—and I kept hearing these words over and over, flowing like an endless stream," Lennon went downstairs and turned it into a song. He began to write the rest of the lyrics and when he was done, he went to bed and forgot about them.

The flavour of the song was heavily influenced by Lennon's and the Beatles' interest in Transcendental Meditation in late 1967 – early 1968, when the song was composed. Based on this he added the mantra "Jai guru deva om" (Sanskrit: जय गुरुदेव ॐ) to the piece, which became the link to the chorus. The Sanskrit phrase is a sentence fragment whose words could have many meanings. Literally it approximates as "glory to the shining remover of darkness,"^[3] and can be paraphrased as "Victory to God divine", "Hail to the divine guru", or the phrase commonly invoked by the late Maharishi Mahesh Yogi in referring to his spiritual teacher "All Glory to Guru Dev."^[4]

The song's lyrical structure is straightforward: three repetitions of a unit consisting of a verse, the line "Jai guru deva om" and the line "Nothing's gonna change my world" repeated four times. The lyrics are highly image-based, with abstract concepts reified with phrases like thoughts "meandering", words "slithering", and undying love "shining". The title phrase "across the universe" appears at intervals to finish lines, although it never cadences, always appearing as a rising figure, melodically unresolved. It finishes on the leading note; to the Western musical ear, the next musical note would be the tonic and would therefore sound complete.

In his 1970 interview with Rolling Stone, Lennon referred to the song as perhaps the best, most poetic lyric he ever wrote: "It's one of the best lyrics I've written. In fact, it could be the best. It's good poetry, or whatever you call it, without chewin' it. See, the ones I like are the ones that stand as words, without melody. They don't have to have any melody, like a poem, you can read them." ^[5]

The song is in the key of D and the verse beginning "Words are flowing out" (I (D) chord) is notable for a prolonged vi (Bm)- iii (F#m) to ii7 (Em7) minor drop to the dominant chord V7 (A7) on "across the universe" in the 4th bar.^[6] On the repeat of this chord sequence a beautiful turn following the ii7 (Em7) through a iv minor (Gm) brings the verse to a close before moving on directly to the tonic on the "Jai Guru Deva Om" refrain. The vi-ii minor drop leading to V had been used earlier in "I Will" (on "how long I've loved you") and George Harrison utilised a shorter vi-iii minor alternation to delay getting back to the dominant (V) in "I Need You".^[6] The verse beginning "Words are flowing out like endless rain..." is also notable for the suitably breathless phrasing and almost constant 8th note rhythm (initially four D melody notes, then C#, B, A, B)^[7]