Wine was a major staple of everyday life for Israel, making the use of vineyards as a symbol of their obedience or disobedience much easier to grasp. It was served to guests when they arrived at dinner, for special occasions, etc. It was meant to be pleasing to the palate. If you've ever tasted a drink that had gone bad or soured, you know an immediate response is to spit it out. This was the problem with Israel's disobedience.
While God, as the Creator, Planter and Pruner of the vines, worked to produce fruit on the branches for others to see and bring Him glory, Israel was becoming drunk on the wine of idolatry. They are described as branches that produced wild grapes or as being dry, barren branches that were eventually removed and destroyed. (Isaiah 5:1-4)
But God doesn't prune them all. There are still branches that produce good fruit and those He cultivated and nourished so that even we, the newly formed family of God, would receive the blessing of being connected to the Vine. In the midst of Isaiah's description of the day of judgment, a song appears about a vineyard. A desirable vineyard. This is in contrast to both the song and the desolate vineyard mentioned earlier in Isaiah. (Isaiah 5:1-7) The desirable vineyard will take root and will eventually "fill the whole world with fruit" (Isaiah 27:6).
What made the difference between the two vineyards?
Friends, God's presence changes everything. The Lord Himself returned to tend this vineyard representing His people, Israel. (Isaiah 27:3) Back in Isaiah 5, the Lord had removed His hand of protection from the vineyard (the hedge). Because of apostasy (rebellion against God) and idolatry (worship of idols), the vineyard was vulnerable to enemy attack and invasion (briers and thorns). (Isaiah 5:5-6) The song about that vineyard is more fitting as a funeral selection. Now, God is no longer upset with Israel and personally keeps and waters the vineyard to ensure its protection and survival. (Isaiah 27:3-4) The song about this vineyard is much sweeter.
It was of utmost importance that Israel followed God's commandments as He had intended for them to bring the world to Him through their example. They were to be the branches connected to the Vine, bearing much fruit and witness of the character of God, thereby bringing Him glory. (Isaiah 5:2-5) Because of their disobedience, they lost out on this honor, and like withered, disconnected branches, they were removed from the Vine. (John 15:2-8) We, as spiritual Israel, have been grafted into the Vine and reap the reward, though not boastfully. (Romans 11:11-12, 15-26)
God in His loving-kindness does not eliminate the whole of His people. Once their guilt has been atoned for, He promises to bring them back to Him. Even His judgment is measured with compassion. (Isaiah 27:7-8) God does not deal with His people with the same judgment as everyone else because His goal is to refine their character. (Hebrews 12:5-11) He will gather them again, and they will once again worship Him, though not as the original group. (Isaiah 27:13) By God's mercy, a new family is formed through the ingrafting of Gentiles (everyone outside of literal Israel), including all who would believe and be connected to the Vine. (Romans 11:11, 17, 19-20) What joy for us who benefit as members of this blended family of God! [While this last statement of a new family blended family is true as explained in light of the New Testament Scriptures, these last verses of Chapter 27 seem to only be talking about regathering the exiled people.]