Is choosing a journal editor in submitting a paper an important step?
Editors could be specialized.

For instance, I work in forecasting, and in an editorial board of a general forecasting journal, some editors may be specialized in sales forecasting, others in macroeconomic forecasting, others in judgmental modifications to forecasts, others in demographics or crime forecasting and so forth. I certainly make an effort to steer my papers towards an editor that is most familiar with my specific topic.

If the editor you picked is not a specialist in your particular topic, he will likely route your submission to an expert colleague on the editorial board, so just picking one should not be too important apart from causing a minuscule amount of additional work. Unless, that is, your abstract does not sound promising to the not-absolute-expert, or the editor you picked is busy, in which case the re-routing could cause a small delay.