ननु नामाविनीतानां विनेतासि परन्तप।
कथमेवंविधं पापं न त्वं शास्सि हि रावणम्॥
nanu nāmāvinītānāṁ vinetāsi parantapa
katham evaṁ-vidhaṁ pāpaṁ na tvaṁ śāssi hi rāvaṇam
nanu nāma = it is well-known that; avinītānām = indisciplined and evil men; vinetā asi = You punish; parantapa = O scorcher of Your foes; katham = how is it that; evam-vidham = like; pāpam = a most sinful person; na = not; tvam = You; śāssi = do punish; hi rāvaṇam = Rāvaṇa.
It is well-known that You punish indisciplined and evil men. O scorcher of Your foes, how is it that You do not punish a most sinful person like Rāvaṇa?1
1 Vinetā asi and na tvaṁ śāssi can also mean “You teach” and “You do not teach” respectively, thereby indicating that according to Mother Sītā, Lord Śrī Rāma teaches indisciplined and evil men [to follow Vedic dharma], and so she wonders how come He didn’t teach a most sinful person like Rāvaṇa [to do the same]. Rāmāyaṇa-bhūṣaṇa: vinetā śikṣakaḥ. pāpaṁ pāpiṣṭham. kathaṁ na śāssi na śikṣayasi.
In the next verse she herself infers the reason for [Lord Rāma] not disciplining [Rāvaṇa then and there].