For Jesus the night was not far away (see ch. 7:33). His brief “day” was the time of His ministry here on earth; the arrival of His night, the time when He would depart out of this world (see ch. 9:5).
While it is day.
That is, the time for labor (Ps. 104:23). The phrase suggests urgency. A similar figure is found in the Mishnah, where Rabbi Tarfon, commenting on the daytime of life, says, “The day is short, and the work [to be performed] is much; and the workmen are indolent, but the reward is much; and the master of the house is insistent” (Aboth 2. 15, Soncino ed. of the Talmud, p. 24).
Textual evidence is divided (cf. p. 146) between this reading and “we must work.” The latter emphasizes the association of the disciples with Jesus in His labors.