For the familiar time phrase In that day, see the comments on 2.11, 20; 3.18; 7.18. The noun day speaks generally of a time in the future.
The remnant of Israel and the survivors of the house of Jacob: These two phrases are parallel, so they refer to the same group of people. For the identification of this group, see the introductory comments on this section [10.20-23]. The term remnant is a technical one and may challenge the translator (see the introduction to this section [10.20-23]). Its basic sense is “something remaining.” In this specific case it refers to a small number of people, left over from a larger group. Here that group consists of those who were taken away as captives by the Assyrians. The parallel expression survivors makes it clear that remnant refers to people “surviving some conflict”—here the Israelites who survived the enemy attack. For survivors see 1.9 and 4.2; for house of Jacob, see 2.5-6 and 8.17.
Will no more lean upon him that smote them, but will lean upon the LORD, the Holy One of Israel, in truth: This gives a picture of dependence. The verb lean upon means to “depend on” or “rely on.” It is not clear what will no more lean upon him that smote them refers to specifically. It may suggest that the Israelites who survived the Assyrian attack on the northern kingdom and who were taken captive to other parts of the empire were now somehow dependent on Assyrian power. They had come to recognize it and affirm it. Thus they were now looking for their support from him that smote them. The pronoun him refers to the Assyrian ruler or his army, and the verb smote (“smite” means “strike/hit”) describes the Assyrian attack on Israel.
When the remnant comes back in the future, they will lean upon the LORD … in truth. Their trust and dependence on Assyria will be replaced by trust in Yahweh. So the prophet sees a return, not just in physical terms, but in religious terms as well. And this return to Yahweh will be in truth, which may be rendered “genuinely” or “completely.” For the Holy One of Israel, see 1.4.
Contemporary English Version reorders this verse, saying “A time is coming when the survivors from Israel and Judah will completely depend on the holy LORD of Israel, instead of the nation that defeated them.” This may a useful model for some languages where this arrangement may be the most natural.
Translation examples for this verse are:
• At that time
the remnant of Israel,
those of Jacob who survive,
will no longer rely on Assyria who defeated them,
but will rely completely on Yahweh, the Holy One of Israel.
• When that time comes those Israelites who are left, those of Jacob who have survived, will no longer depend on the Assyrians who defeated them. Rather, they will depend utterly on Yahweh, the Holy One of Israel.
Quoted with permission from Ogden, Graham S. and Sterk, Jan. A Handbook on Isaiah. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here .