Jamieson, Fausset and Brown on James 4:13

13. Go to now--"Come now"; said to excite attention.

ye that say--boasting of the morrow.

To-day or to-morrow--as if ye had the free choice of either day as a certainty. Others read, "To-day and to-morrow."

such a city--literally, "this the city" (namely, the one present to the mind of the speaker). This city here.

continue ... a year--rather, "spend one year." Their language implies that when this one year is out, they purpose similarly settling plans for to come [Bengel].

buy and sell--Their plans for the future are all worldly.