Before there was rain, before there was agriculture, there was a waiting earth. Targum Pseudo-Jonathan on (Genesis 2:5) explains the pause: "all the trees of the field were not as yet in the earth, and all the herbs of the field had not as yet germinated, because the Lord God had not made it to rain upon the earth, and man was not to cultivate the ground."
The Targumist pairs two absences: no rain, no human being. Both are required for the field. God will bring the water; humanity will bring the work. Creation is explicitly designed to leave room for human partnership. The field is not finished until someone shows up to plant it.