Hibiscus flowers are not offered in general.
Shall give a detailed explanation of this pasuram later, it denotes that Perumal is the antaryami.
While the Lord is omnipresent, here “un AgathAn” denotes Siva resides in one part of Perumal. An explanation of this pasuram shall be provided later.
Chakratazhwar is also eternal, and He has also incarnated like Sri Rama and Krishna, hence we celebrate His incarnation day as Sudarshana Jayanti.