Jamieson, Fausset and Brown on Luke 2:40

40. His mental development kept pace with His bodily, and "the grace of God," the divine favor, rested manifestly and increasingly upon Him. See Lu 2:52.

Lu 2:41-52. First Conscious Visit to Jerusalem.

"Solitary flowered out of the wonderful enclosed garden of the thirty years, plucked precisely there where the swollen bud, at a distinctive crisis (at twelve years of age), bursts into flower. To mark that is assuredly the design and the meaning of this record" [Stier].