Genesis 4:3
“And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the Lord.”
KJV
Read in Genesis 4Meaning
Cain brings produce from his work as an offering to the LORD. Worship is already part of the brothers' life outside Eden.
Read carefully
The text does not state here that Cain's offering was rejected because it was plant produce; later interpretation should not invent a reason the verse does not give.
Reflection
The verse directs attention beyond the mere existence of a religious act toward the character and response of the worshiper in the verses that follow.