My quick reaction:
This open letter and another one by serving soldiers published in May, quickly condemned by the Macron government, expose a growing fissure in French society. I suspect it was not a coincidence that the letters came out while Marine Le Pen was leading Macron in the first round polls for next year's presidential election. Even though Le Pen's lead has largely vanished, she is still hot on Macron's heels in the second round polls. The ascent of Xavier Bertrand as the leader of the center right has complicated the picture, but the French presidential election will be the most important event on the European calendar in 2021.