There is a clear allusion in this one passage (a) that the Lord formed the Church, and (b) that His Word is open and understandable. The proximity of these two elements is a clear rebuke to those who say that God's word is not clear, and that somehow a Magisterium is needed to interpret it:
"I am the LORD, and there is no other.
I did not speak in secret,
in a land of darkness;
I did not say to the offspring of Jacob,
'Seek me in vain.'
I the LORD speak the truth;
I declare what is right.
"Assemble yourselves and come;
draw near together,
you survivors of the nations!
They have no knowledge
who carry about their wooden idols,
and keep on praying to a god
that cannot save.
Declare and present your case;
let them take counsel together!
Who told this long ago?
Who declared it of old?
Was it not I, the LORD?
And there is no other god besides me,
a righteous God and a Savior;
there is none besides me.
"Turn to me and be saved,
all the ends of the earth!
For I am God, and there is no other.
By myself I have sworn;
from my mouth has gone out in righteousness
a word that shall not return:
'To me every knee shall bow,
every tongue shall swear allegiance.'
"Only in the LORD, it shall be said of me,
are righteousness and strength;
to him shall come and be ashamed
all who were incensed against him.
In the LORD all the offspring of Israel
shall be justified and shall glory."
(From Isaiah 45:18-25)
Note what commentator J. Alec Motyer says: "the world vision of verses 14–17 is to be understood in the light of revelation. In quiet rebuke of the allegation (Is. 45:15) that he 'hides himself', the Lord asserts that he never spoke in secret (lit. 'under cover'): his word was openly available; nor in a land of darkness where one might lose one's way: his word was intrinsically plain and straightforward; and it led them straight to himself: his word was not in vain, [it was] solid ground not shifting sand. What he said was truth and right: the former is 'righteousness', conformity to the absolute norm of divine truth; the latter is 'plain, straightforward', without deviance or duplicity.
(from J. Alec Motyer, "Isaiah," Tyndale Old Testament Commentaries, 290-291)
God’s word does not need a Magisterium to interpret it. He does not speak “under cover”. His word was intrinsically plain and straightforward; it leads straight to himself.