Then in that day the remnant of Israel and those of the house of Israel who have escaped will no longer rely upon him who strikes them—the king of Assyria—but they will rely upon Jehovah, the Holy One of Israel, in truth (v. 20). To rely upon Jehovah in truth is to rely upon Him in honesty.
Verses 21 and 22a go on to say, "A remnant will return, the remnant of Jacob, to the mighty God. For though your people, O Israel, are like the sand of the sea, only a remnant among them will return." This word is quoted by Paul in Romans 9:27. The reason that only a remnant will return is given in Isaiah 10:22b-23. "Annihilation is strictly decided, overflowing with righteousness. For utter destruction and a strict decision is Jehovah of hosts performing in the midst of the whole land."
In verse 24 Jehovah tells His people dwelling in Zion not to fear Assyria, which strikes with the rod and lifts up the staff against them the way Egypt did. Then in the following verses Jehovah says, "For in a very little while My indignation will be completed, and My anger will be turned toward their destruction. And against them Jehovah of hosts will rouse up a whip like the stroke against Midian at the rock of Oreb; and His staff will be over the sea, and He will lift it up the way He did in Egypt. And in that day their burden will be removed from your shoulders, and their yoke from off your neck; and the yoke will be broken due to the fatness" (vv. 25-27). From this we see that God's judgment will eventually issue in the return of His people.