L. was born circa 1875 in Cherkassy, Kiev Gubernia, Ukraine. His father was a melamed (religious teacher). Until the age of seventeen he learned Talmud, then as an extern he completed a gymnasium. From 1902 until 1905 he studied in Paris.

He began his political societal activities as a Zionist of the Ekhud-hems system, and L. was then one of the first activists of the proletariat Zionists (Po‘ale Tsiyon). In 1903 he belonged to the group of Zionist socialists who organized the conference of "Vozrozhdenye (Rebirth)", later he became one of the major leaders of the S"S party (Zionist socialists), from where there crystallized the "Vozrozhdenye". During the World War he took an active part in the hilfs-arbet, participating in the hilfs-baratung in Peterburg (1916).

After the March Revolution -- one of the founders and leaders of the party "Fareynikte". In May 1919 he directed the division in his party and as a leader of his ofgeshfaltenem wing, they cast it together with the Communist Bund (Kombund) into one organization (Komfarband, or the Jewish Communist Union), and since then has continued one of the important Jewish communist leaders in the Soviet Union and editor of "Emes".

L. has always participated as a contributor and often as an editor in the various periodical publications that were issued through the party to which he has belonged.