Line upon Line
Admonition or instruction repeated little by little (a line at a time). Apelles said “Nulla dies sine linea. ” A drawing is line upon line, an edifice is brick upon brick or stone upon stone.
“Line upon line, line upon line, here a little and there a little.” - Isiah xxviii. 10.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894