nimittam param isasya
hiranyagarbhah sarvas ca
Even Lord Brahma and Lord Siva act only as Your instruments in cosmic creation and annihilation, which are ultimately done by You, the Supreme Lord, in Your invisible aspect of time.
Uddhava here explains that in fact Lord Krsna Himself will cause the death of Jarasandha, and Bhima will merely be the instrument. The Supreme Lord, through His invisible potency of time, creates and annihilates the entire cosmic situation, whereas great demigods such as Lord Brahma and Lord Siva are merely the instruments of the Lord’s will. Therefore Bhima will have no difficulty acting as the Lord’s instrument to kill the powerful Jarasandha. In this way, by the Lord’s arrangement, His devotee Bhima will be glorified.