Same God, Same basis for Salvation

Compare Isaiah's preaching a call to repentance, to Paul's teaching in Eph and Col.

And you He made alive, who were dead in trespasses and sins, in which you once walked according to the course of this world, according to the prince of the power of the air, the spirit who now works in the sons of disobedience, among whom also we all once conducted ourselves in the lusts of our flesh, fulfilling the desires of the flesh and of the mind, and were by nature children of wrath, just as the others.
Ephesians 2:1‭-‬3 NKJV

Therefore put to death your members which are on the earth: fornication, uncleanness, passion, evil desire, and covetousness, which is idolatry. Because of these things the wrath of God is coming upon the sons of disobedience, in which you yourselves once walked when you lived in them.
Colossians 3:5‭-‬7 NKJV

This is how God, through Isaiah, promised a Messiah who will cleanse us from our Sins IF we are willing to obey (repentance).

“Wash yourselves, make yourselves clean; Put away the evil of your doings from before My eyes. Cease to do evil, Learn to do good; Seek justice, Rebuke the oppressor; Defend the fatherless, Plead for the widow. “Come now, and let us reason together,” Says the Lord , “Though your sins are like scarlet, They shall be as white as snow; Though they are red like crimson, They shall be as wool. If you are willing and obedient, You shall eat the good of the land; But if you refuse and rebel, You shall be devoured by the sword”; For the mouth of the Lord has spoken.
Isaiah 1:16‭-‬20 NKJV