Purport

In earlier Shlokas, Bhagvan Shri Krishna described how many humans worship different deities to fulfill their worldly desires. Since this arrangement of deities being the caretaker of humans for physical needs been fixed at the start of the universe (Ch3: Sh10-11), human does get the fruits of worshipping deities.

In this Shloka Bhagvan Shri Krishna describes the secret that in reality such fruits are also given by Him(Shri Krishna). This can be understood better when reading with Shloka Ch4: Sh11, in which Bhagvan Shri Krishna described that in reality, all deities too are the manifestation of him alone. Worshipping to any deity hence finally reach to him. Every path of worship finally reaches Bhagavan Shri Krishna as different rivers finally merge in Ocean.

"All, who worship me in whatever forms of me(means deities), I reward them accordingly as all men ultimately follow my path in all respects, O son of Parth(Arjuna)."

All worship to any deities finally reach to Bhagvan Shri Krishna and all fruits to such worship ultimately come from Shri Krishna alone.