It is considered that the Sanze-isshin Law was established as a special measure especially to urge cultivation of rice fields because there were no regulations concerning the cultivation in the Denryo (the law about providing rice fields) of the existing Yoro Ritsuryo code.
現存する養老律令の田令には、農地開墾に関する規定がないことから、特に墾田を推奨するため、三世一身法を特別措置法的に定めたものと考えられる。