L. Berkhof sums it up well,
Now the question can be raised, How can we then be urged to watch for the coming? Jesus teaches us in Matt. 24:32,33 to watch for the coming through the signs: “when ye see all these things, know ye that He is nigh.” Moreover, we need not interpret the exhortation to watch as an exhortation to scan the heavens for immediate signs of the Lord’s appearance. We should rather see in it an admonition to be awake, to be alert, to be prepared, to be active in the work of the Lord, lest we be overtaken by sudden calamity. (emphases mine; Systematic Theology p. 697).
