Albert Barnes Commentary Isaiah 8:18

"Behold, I and the children whom Jehovah hath given me are for signs and for wonders in Israel from Jehovah of hosts, who dwelleth in mount Zion." — Isaiah 8:18 (ASV)

Behold, I... - By ‘signs and wonders,’ here, it means that these individuals, through the names given to them, were intended to teach important lessons to the Jewish people. Their names were significant and were designed to illustrate some important truth. Especially, the prophet here suggests that these names were to instill the truth regarding the presence and protection of God, to encourage the people to look to Him.

Thus, the name Immanuel, ‘God with us’ (Isaiah 7:14), and Shear-jashub, ‘the remnant shall return’ (Isaiah 7:3), were both significant of the fact that only God could be the protector of the nation. Similarly, it is possible that his own name, signifying ‘the salvation of Jehovah,’ had been given him with such a reference. But in any case, it was a name that would remind them of the truth he was now teaching: that salvation was to be found in Yahweh, and that they should look to Him.

Names of children were often emblematic in this way ; and the prophets themselves were regarded as signs of important events (Ezekiel 24:24); compare the note at Isaiah 20:3. This passage is quoted with reference to the Messiah in Hebrews 2:13.

Which dwelleth in mount Zion - Mount Zion was the residence of the house of David, or of the court, and it was often used to signify Jerusalem itself. The meaning here is that God was the protector of Jerusalem, or regarded that as His home (see the note at Isaiah 1:8).