法華玄贊義決 1.284

1.284

如疏釋。又助釋云：無學後心世間三昧說為化城，如二車體，以根本智不作解故，後得智作涅槃想解將為究竟，經化作故。論云第四人者，方便令入涅槃城故；涅槃城者，諸禪三昧城故。

It is as explained in the commentary. In addition, an auxiliary explanation states: the worldly samādhis of the subsequent mind of an aśaikṣa are spoken of as the phantom city, just like the essence of the two carts. Because the fundamental wisdom does not make this understanding, the subsequently attained wisdom generates the notion and understanding of nirvāṇa, taking it to be ultimate, [yet it is] phantasmally created by the sūtra. The treatise states that as for the fourth person, it is in order to expediently cause them to enter the city of nirvāṇa; the city of nirvāṇa is the city of the various dhyānas and samādhis.