פירוש על ברכות 107:6

It has been suggested that this exhortation is directed against Sadducean teaching; cf. Lehmann in R. E. J. xxxi. pp. 31 ff.

The idea of two is derived from the spelling of the word for "heart" — לבבך instead of לבך; see A. P. A. ii. p. 15 n. 3.