oldArray references [1, 2, 3], so if you remove the following line:
newArray = oldArray;
you are left with the following code:
newArray = oldArray.concat(concatMe);
The above code concatenates concatMe which references [4, 5, 6] to the end of oldArray
It is just the starting code. The challenge expects you to either delete or not. It does not change the outcome. If you leave it in or delete the above line, newArray still becomes [ 1, 2, 3, 4, 5, 6 ]
If you instead place the same line (newArray = oldArray;) below the last line ( newArray = oldArray.concat(concatMe);), then newArray will be [1, 2, 3].