Does it matter since sin is a universal issue?
Sin (transgression out of rebellion) IS a universal issue.
That IS a universal Principle.
While, what determines what is a trangression is a Dispensational issue - who, what, when, where, why, and how...
Note the Principle BUT ALSO the Dispensational Rule of Thumb...
Luke 12:42 And the Lord said, Who then is that faithful and wise steward, whom his lord shall make ruler over his household, to give them their portion of meat in due season?
Case in point of many that could be cited - Gen. 9:3 IN CONTRAST TO Lev. 11:3, and that, in turn, IN CONTRAST TO 1 Tim. 4:4.
Genesis 9:3 Every moving thing that liveth shall be meat for you; even as the green herb have I given you all things.
Leviticus 11:4 Nevertheless these shall ye not eat of them that chew the cud, or of them that divide the hoof: as the camel, because he cheweth the cud, but divideth not the hoof; he is unclean unto you.
1 Timothy 4:4 For every creature of God is good, and nothing to be refused, if it be received with thanksgiving: 4:5 For it is sanctified by the word of God and prayer.
Where does Isaiah 1:18 fit within all this as to who, what, when, where, why, and how - well, since he wrote it; why don't we just ask him?
Isaiah 1:1 The vision of Isaiah the son of Amoz, which he saw concerning Judah and Jerusalem in the days of Uzziah, Jotham, Ahaz, and Hezekiah, kings of Judah. 1:2 Hear, O heavens, and give ear, O earth: for the LORD hath spoken, I have nourished and brought up children, and they have rebelled against me. 1:3 The ox knoweth his owner, and the *** his master's crib: but Israel doth not know, my people doth not consider. 1:4 Ah sinful nation, a people laden with iniquity, a seed of evildoers, children that are corrupters: they have forsaken the LORD, they have provoked the Holy One of Israel unto anger, they are gone away backward. 1:5 Why should ye be stricken any more? ye will revolt more and more: the whole head is sick, and the whole heart faint. 1:6 From the sole of the foot even unto the head there is no soundness in it; but wounds, and bruises, and putrifying sores: they have not been closed, neither bound up, neither mollified with ointment. 1:7 Your country is desolate, your cities are burned with fire: your land, strangers devour it in your presence, and it is desolate, as overthrown by strangers. 1:8 And the daughter of Zion is left as a cottage in a vineyard, as a lodge in a garden of cucumbers, as a besieged city. 1:9 Except the LORD of hosts had left unto us a very small remnant, we should have been as Sodom, and we should have been like unto Gomorrah. 1:10 Hear the word of the LORD, ye rulers of Sodom; give ear unto the law of our God, ye people of Gomorrah. 1:11 To what purpose is the multitude of your sacrifices unto me? saith the LORD: I am full of the burnt offerings of rams, and the fat of fed beasts; and I delight not in the blood of bullocks, or of lambs, or of he goats.
Let's ask another witness as to who Isaiah was taking about...
Hmm; what Principle is that?
Matthew 18:16 But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established.
What say you, Apostle Paul?
Romans 9:1 I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost, 9:2 That I have great heaviness and continual sorrow in my heart. 9:3 For I could wish that myself were accursed from Christ for my brethren, my kinsmen according to the flesh: 9:4 Who are Israelites; to whom pertaineth the adoption, and the glory, and the covenants, and the giving of the law, and the service of God, and the promises; 9:5 Whose are the fathers, and of whom as concerning the flesh Christ came, who is over all, God blessed for ever. Amen. 9:6 Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel: 9:7 Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called.
Rom 9:27 Esaias also crieth concerning Israel, Though the number of the children of Israel be as the sand of the sea, a remnant shall be saved: 9:28 For he will finish the work, and cut it short in righteousness: because a short work will the Lord make upon the earth. 9:29 And as Esaias said before, Except the Lord of Sabaoth had left us a seed, we had been as Sodoma, and been made like unto Gomorrha.
In short, Isaiah's issue is that of Israel under the Law...
2 Chronicles 7:14 If my people, which are called by my name, shall humble themselves, and pray, and seek my face, and turn from their wicked ways; then will I hear from heaven, and will forgive their sin, and will heal their land.
Isaiah 43:22 But thou hast not called upon me, O Jacob; but thou hast been weary of me, O Israel. 43:23 Thou hast not brought me the small cattle of thy burnt offerings; neither hast thou honoured me with thy sacrifices. I have not caused thee to serve with an offering, nor wearied thee with incense. 43:24 Thou hast bought me no sweet cane with money, neither hast thou filled me with the fat of thy sacrifices: but thou hast made me to serve with thy sins, thou hast wearied me with thine iniquities. 43:25 I, even I, am he that blotteth out thy transgressions for mine own sake, and will not remember thy sins. 43:26 Put me in remembrance: let us plead together: declare thou, that thou mayest be justified. 43:27 Thy first father hath sinned, and thy teachers have transgressed against me. 43:28 Therefore I have profaned the princes of the sanctuary, and have given Jacob to the curse, and Israel to reproaches.