CC Madhya 14.18
bhṛtyera bhṛtya kara, — ei mora āśa
The greatest achievement for a devotee is to become a servant of the servants of the Lord. Actually, no one should desire to become the direct servant of the Lord. That is not a very good idea. When Prahlāda Mahārāja was offered a benediction by Nṛsiṁhadeva, Prahlāda rejected all kinds of material benedictions, but he prayed to become the servant of the servants of the Lord. When Dhruva Mahārāja was offered a benediction by Kuvera, the treasurer of the demigods, Dhruva could have asked for unlimited material opulence, but he simply asked for the benediction of becoming the servant of the servants of the Lord. Kholāvecā Śrīdhara was a very poor man, but when Śrī Caitanya Mahāprabhu wanted to give him a benediction, he also prayed to the Lord to be allowed to remain a servant of the servants of the Lord. The conclusion is that being the servant of the servants of the Supreme Personality of Godhead is the highest benediction one can desire.