SB 10.71.3

yaṣṭavyam rājasūyena
 dik-cakra-jayinā vibho
ato jarā-suta-jaya
 ubhayārtho mato mama
Synonyms: 
yaṣṭavyam — sacrifice should be performed; rājasūyena — with the Rājasūya ritual; dik — of directions; cakra — the complete circle; jayinā — by one who has conquered; vibho — O almighty one; ataḥ — therefore; jarā-suta — of the son of Jarā; jayaḥ — the conquest; ubhaya — both; arthaḥ — having the purposes; mataḥ — opinion; mama — my.
Translation: 
Only one who has conquered all opponents in every direction can perform the Rājasūya sacrifice, O almighty one. Thus, in my opinion, conquering Jarāsandha will serve both purposes.
Purport: 

Śrī Uddhava here explains that only one who has conquered all directions is entitled to perform the Rājasūya sacrifice. Therefore Lord Kṛṣṇa should immediately accept the invitation to participate in the sacrifice, but then He should arrange to kill Jarāsandha as a necessary prerequisite. In this way the kings’ request for protection would be fulfilled automatically. If the Lord would thus adhere to a single policy — namely, seeing that the Rājasūya sacrifice was performed properly — all purposes would be fulfilled.

According to Śrīla Rūpa Gosvāmī in his Bhakti-rasāmṛta-sindhu, one of Lord Kṛṣṇa’s qualities is catura, “clever,” which means that He can perform various types of work at the same time. Thus the Lord could certainly have solved the dilemma of how to simultaneously satisfy King Yudhiṣṭhira’s desire to perform the Rājasūya sacrifice and the imprisoned kings’ desire for freedom. But Kṛṣṇa wanted to give His dear devotee Uddhava the credit for the solution, and thus He pretended to be perplexed.