Isaiah continues to describe the time when God will save the people of Israel. Although these events will happen in the future ([Isaiah 9:1](./01.md)), Isaiah describes them as if they have already happened. This emphasizes that they certainly will happen. (See: [[rc://en/ta/man/translate/figs-pastforfuture]])
These two phrases mean basically the same thing. The word "us" refers to both the speaker and the hearer and so is inclusive. This can be stated in active form. Alternate translation: "For the Lord will give to us a child" (See: [[rc://en/ta/man/translate/figs-parallelism]] and [[rc://en/ta/man/translate/figs-exclusive]] and [[rc://en/ta/man/translate/figs-activepassive]])
His authority to rule is spoken of as if it were the robe that is a symbol of his authority. Alternate translation: "he will wear his royal robe on his shoulder" or "he will have authority to rule as king." (See: [[rc://en/ta/man/translate/figs-metaphor]])