CC Ādi 16.38

tomāra kavitā śloka bujhite kāra śakti
tumi bhāla jāna artha kiṁvā sarasvatī
Word for word: 
tomāra — your; kavitā — poetry; śloka — verses; bujhite — to understand; kāra — whose; śakti — power; tumi — you; bhāla — well; jāna — know; artha — meaning; kiṁvā — or; sarasvatī — the goddess of learning.
Translation: 
“Your poetry is so difficult that no one can understand it but you and mother Sarasvatī, the goddess of learning.
Purport: 

Replying to Keśava Kāśmīrī sarcastically, Lord Caitanya Mahāprabhu indirectly minimized the value of his poetry by saying, “Yes, your compositions are so nice that no one but you and your worshipable mother, the goddess of learning, can understand them.” Keśava Kāśmīrī was a favorite devotee of mother Sarasvatī, the goddess of learning, but Caitanya Mahāprabhu, as the master of the goddess of learning, has the right to speak sarcastically of her devotees. In other words, although Keśava Kāśmīrī was proud of being favored by the goddess of learning, he did not know that she is controlled by Caitanya Mahāprabhu Himself because He is the Supreme Personality of Godhead.