अदृष्टपूर्वं हृषितोऽस्मि दृष्ट्वा भयेन च प्रव्यथितं मनो मे। तदेव मे दर्शय देव रूपं प्रसीद देवेश जगन्निवास ॥

adṛiṣhṭa-pūrvaṁ hṛiṣhito ’smi dṛiṣhṭvā bhayena cha pravyathitaṁ mano me tad eva me darśhaya deva rūpaṁ prasīda deveśha jagan-nivāsa

I have seen that which none hath seen before, My heart is glad, yet faileth me for fear; Show me, O God, Thine other Form again— Mercy, O God of Gods, home of all worlds—

In plain words: Arjuna says he has seen what no one has seen before. He is glad, but his heart is shaking with fear, so he begs Krishna to show his other, gentler form again.