“you shall above all things be glad and young”

(sometimes numbered or referred to as poem 22) by E. E. Cummings.

It begins with the lines you recalled (phrased as “you shall above all things be glad and young”) and continues in Cummings’s characteristic style—lowercase letters, unconventional spacing/punctuation, and playful wordplay. It urges the addressee to stay joyful and youthful in spirit, notes that youth and gladness transform whatever life brings, includes a passage about love and mystery, and ends with the memorable preference for learning song from one bird over teaching stars not to dance.

The poem appears in collections of his work (such as Selected Poems and the complete poems editions). Because Cummings’s works remain under copyright, the full text isn’t reproduced here; you can find it in standard published editions or reliable poetry sites/anthologies that have permission.