Bhagavad Gita 11.54

Only through tireless devotion can I be seen and known; only in this way can a person become one with Me, O Arjuna!

भक्त्या त्वनन्यया शक्यमहमेवंविधोऽर्जुन।
ज्ञातुं दृष्टुं च तत्त्वेन प्रवेष्टुं च परंतप॥

bhaktyā tvananyayā śakyamahamevaṃvidho'rjuna|
jñātuṃ dṛṣṭuṃ ca tattvena praveṣṭuṃ ca paraṃtapa||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).