Isaiah and the Davidic Line

Isaiah was a covenant representative of God, as were all authoritative Old Testament prophets (just like the New Testament apostles). As such, his primary role was to act as God's emissary to God's people, prosecuting the terms of the covenant. In plain language, this means that Isaiah was responsible for knowing what the terms of God's covenant with his people were, for letting the people know whether or not they were complying with those terms (they usually were not complying), and for encouraging them in various ways to keep the terms of the covenant (e.g. offering blessings for obedience and threatening curses for disobedience). So, Isaiah's view of God's protection of the Davidic king and Jerusalem were based on his understanding of God's covenant obligations regarding these. His views of the people's traditions regarding these same things were based on how well these traditions compared to the truth.

The Davidic covenant was the covenant that God made with David in 2 Samuel 7. We also find details of this covenant in Psalms 89 and 132, as well as a very important tidbit in 2 Chronicles 6:16. This covenant was an administration of the same covenant that God had previously maintained under Adam, Noah, Abraham, and Moses. As such, it included all the stipulations (laws, conditions, etc.) of the prior administrations of the covenant. It also extended the offers of blessing to include a Davidic king over Israel. This kingship was a blessing for David in that it honored him and gave him and his descendents significant power. But it was also a blessing for Israel in that a righteous Davidic king would give the nation great stability and international power, as well as lead the nation in covenant fidelity so that all Israelites would inherit the covenant blessings.

So, Isaiah viewed the Davidic covenant as God's offer to provide a Davidic king for Israel on the condition that the Davidic king remained obedient to God's law (i.e. to the stipulations of the covenant). Each although the Davidic covenant remained perpetually in force, each individual Davidide was responsible before God on behalf of the people. Isaiah, therefore, rightly considered it his responsibility to call the Davidic kings to be accountable to God's law (both for the kings' benefit and for the nation's benefit). As Isaiah saw what the Davidic kings did, and compared their actions to the requirements of the covenant, he was able to advise, exhort, rebuke, warn and encourage them to greater faithfulness.

Isaiah's understanding of Jerusalem was very similar to his understanding of the Davidic covenant and Davidic kingship. Specifically, God's offer to maintain his house and presence in Jerusalem was conditional - only if the people remained faithful to God would God continue to protect them and to dwell among them there. In the course of history, Judah (and Israel) failed to remain faithful, and was (were) exiled from the Promised Land and from Jerusalem. Isaiah knew this was a possibility during the years of his ministry, and warned that Jerusalem would fall because of Judah's wickedness (e.g. Isa. 62:4; 64:8-10). But he also believed that God had long-term goals for Jerusalem he would bring to fruition during the restoration when God would cause many people to be faithful to him (thereby causing them to keep the covenant and to gain the covenant blessings). This hope for Jerusalem is evident throughout the latter chapters of the book. Ultimately, the restoration of Jerusalem that Isaiah prophesied will not be fulfilled until Jesus returns (Rev. 21:2).

Probably, the fact that the people did not appropriately heed Isaiah's messages indicates that their own traditions regarding Davidic kingship and Jerusalem were erroneous. It does appear that by the time of Jeremiah's ministry (perhaps 100 years or so after Isaiah was written), the traditions regarding the temple had begun to misinterpret God's protection and covenant blessings as unconditional rather than conditional (Jer. 7:4). It is not unlikely that such errors also existed in Isaiah's day.