The foreigners who go to Belgium from Christmas Day must be able to show a negative result of a coronat test. There are special border controls for that. The results must not be more than two days old.
The measure was introduced to prevent foreigners from shopping in Belgium because the shops are still open there. In the Netherlands, among others, the non-essential shops are closed in order to prevent further spread of the coronavirus.
Belgium feared last weekend an influx of Dutch people who wanted to buy gifts there just before Christmas. However, large crowds in popular shopping cities such as Antwerp and Knokke remained out.