Isaiah 10:16-17 KJB
Isaiah wrote these verses in the middle of his prophecy that God would destroy the wicked nation of Assyria. But these two verses look forward to God's eventual destruction of all evil, and His salvation of humanity.
God's "fat ones" would be all of God's people whom He will bless. God will send "leanness" to them to spiritually shape them up and get them ready for His coming final war against evil and the Devil. God will empower them with His fire to be able to spread His gospel to the whole world, as He did on the day of Pentecost. Acts 2:1-4 (KJB). The Apostle John seems to have prophesied that the Church at Philadelphia, which would symbolize the final universal Church in the last days of the Church Age, God will provide with an "open door" which cannot be shut to preach the gospel to the whole world just before Christ Raptures His Church. Revelation 3:1-11; Matthew 24:14 (KJB). The Church at Laodicea might be a half-hearted and lukewarm attempt to continue the Church into at least the first 31/2 years of the Tribulation period.
Fire has two purposes. It can destroy, and it can give some light and heat. God lit a fire in the Israelites to light the world by writing His Word and bringing His Messiah into the world. But the "Holy One," who is the Messiah, became God's greatest flame because He became the "Light of the world" who, through His sacrifice and resurrection, will save His entire, living human race from eternal death which the Devil desires to inflict on them. II Timothy 1:10; I Corinthians 15:26; I John 3:8; I Timothy 4:10 (KJB). As He does throughout the Bible, God refers to evil as being like "thorns" and "briers." When living humans become saved by God's grace, He annuls their spiritual deaths, and He gives them the everlasting and perfect righteousness of Christ Himself. John 3:3; John 5:24; II Corinthians 5:21 (KJB). But the "thorns" and "briers" and "tares," which symbolize evil, still cling to all living humans whom God must consign to one of the three regions of death when they die because God cannot accept the filthiness of sin and evil. But Christ will visit all unbelievers "on the earth, and under the earth" in the end of the world, and He will cause them all to repent and return to the faith in Him as their Savior that He put into them when He created them. Genesis 1:31; Genesis 1:26-27 (KJB). Christ will then use His fiery wrath against evil to dissolve their beings to separate their "thorns" and "tares," which are their evil and spiritual deaths, from their repentant, living natures so that He can save and recreate their living natures, and He will cast their dead and evil natures into the eternal lake of fire. Isaiah 10:16-17; Matthew 13:36-43; Luke 3:16-17; I Corinthians 3:11-15; II Peter 3:9-13; Revelation 5:11-14; Revelation 20:5; Revelation 20:11-15; Revelation 21:1-5 (KJB).
Christ never changes. Hebrews 13:8 (KJB). His Love and compassion never fail. I Corinthians 13:8 (KJB). Christ will have just as much compassion to save repentant sinners after their physical deaths as He does for those who repent while physically alive. John 11:25-26; John 5:28-29; II Peter 3:9; I Timothy 2:4; Revelation 5:11-14; I Timothy 4:10 (KJB). God can never lose anything He has ever created. Ecclesiastes 3:14; Psalm 111:7-8 (KJB).