Canto 3 -
Araṇya-kāṇḍa
Chapter 37: Mārīca Advises Rāvaṇa
Text 3.37.18

अप्रमेयं हि तत्तेजो यस्य सा जनकात्मजा।
न त्वं समर्थस्तां हर्तुं रामचापाश्रयां वने॥

aprameyaṁ hi tat-tejo yasya sā janakātmajā
na tvaṁ samarthas tāṁ hartuṁ rāma-cāpāśrayāṁ vane

aprameyam = is immeasurable; hi = indeed; tat-tejaḥ = prowess; yasya = the prowess of Him who is related to; = the; janaka-ātmajā = daughter of Janaka; na = not; tvam = you; samarthaḥ = are capable; tām = her; hartum = of carrying; rāma-cāpa-āśrayām = [for] she is under the shelter of Rāma’s bow; vane = in the forest.

Indeed, the prowess of Him who is related to the daughter of Janaka, is immeasurable. You are not capable of carrying her [for] she is under the shelter of Rāma’s bow in the forest.

[Here] Lord Rāma has been described as being excellent by dint of His relationship with Sītā-devī in accordance with the statement:

śraddhayā devo devatvam aśnute

“The Lord is the Lord because of Śraddhā-devī.”1 (Taittirīya-brāhmaṇa 3.12.3.1)

“In the forest” means “in a carefully protected place.” Rāma-cāpāśrayām (“who is under the shelter of Rāma’s bow”) speaks of Śrī Rāma’s glory. In other words, she cannot be carried due to both these reasons.2 Janakātmajā (“daughter of Janaka”) indicates that by dint of the power of her lineage she cannot be carried away.3

1 Śraddhā is one of the names of Śrī as she herself informs Indra in Mahābhārata 12.221.21-22: ahaṁ lakṣmīr ahaṁ bhūtiḥ śrīś cāhaṁ bala-sūdana, ahaṁ śraddhā ca medhā ca san-natir vijitiḥ sthitiḥ; ahaṁ dhṛtir ahaṁ siddhir ahaṁ tviḍ bhūtir eva ca, ahaṁ svāhā svadhā caiva saṁstutir niyatiḥ kṛtiḥ. (BORI edition)

2 The first reason was stated in text 14 and the second reason is stated in the current text. 

3 Sītā-devī was born in the dynasty of Janaka. Therefore, she cannot be carried away. This is the third reason that Mārīca gives to Rāvaṇa for why she cannot be kidnapped.