Beginning with 1810, he, as a rich and influential merchant, was entrusted, together with Abraham Prinz and Solomon Reuben, with the responsibility of forwarding to Palestine the contributions which were sent annually to Amsterdam.
When, in 1829, the congregation of the Ashkenazim in Jerusalem had become involved in financial difficulties through the building of a new synagogue and school, and was obliged to appeal for support to its coreligionists in Europe, Lehren, as president of the Ḥaluḳḳah committee, prohibited in a harshly-worded circular the transmission of any further contributions to Jerusalem.
In his defense Lehren published "Drei Briefe aus Jerusalem zur Vertheidigung der Ehrlichkeit des Amsterdamer Comité's in Betreff der Palästinaspenden" with the Hebrew title "Ḳonṭres Emet me-Ereẓ" (part i., Amsterdam, 1843; part ii., ib.
1844), after he had already published the Hebrew article of Solomon Kohen, "Emet me-Ereẓ," with the German title "Sendschreiben oder Wahrheit aus dem Heiligen Lande" (ib.
The letters of recognition for this service, sent to Lehren and Prinz by many rabbis, were published under the title "Torat ha-Ḳena'ot" (ib.