In Vayikra 25:3 it says:
שש שנים תזרע שדך ושש שנים תזמור כרמך
Why does it say twice שש שנים ?
in the Sifra (Behar):
To understand the Midrash Tanaim, I looked in the commentary of Rabbi Aaron Iben Chaim - called "Korban Haaron" (Lived in Fez about four hundred and fifty years) the book is strongly recommended.
The Sifra ask: Can we pick up (in the seventh year) all the corn planted in the sixth year?
answer : six year it says twice, the second
Because the book is not common I am attaching a picture of him :
There is certainly a derasha, as given in the other answer. But on a peshat level, there is also a straightforward answer. It is beautiful and poetic. And it resonates. There is a certain Biblical style here, carried through in the next phrases and in the next verses. This is carried out by meter, syllable count, by parallelism, and repeated syntactic structure within the parallelism.