The question is:
“What is, in your opinion, the best argument supporting the doctrine of the perspicuity of Scripture ?”
Notes :
For the supporters of the perspicuity:
.
Well, the thread has at present the problem that contributions
have not come so far from supporters of the doctrine under scrutiny. So at this point let’s quote an academical source
www.tms.edu/tmsj/tmsj15i.pdf ( together with brief commentaries of mine in blue)
*Support of Perspicuity
The doctrine of the perspicuity of Scripture pervades the Bible, as the following chart displays:
Biblical Teaching about the Perspicuity of Scripture
Scripture is light.“Your word is a lamp to my feet and alight to my path” (Ps 119:105).“And we have something more sure, theprophetic word, to which you will do well to pay attention as to a lamp shin-ing in a dark place . . .” (2 Pet 1:19a).
That Scripture tells us that parts of Scripture are as a lamp
does not amount to a statement about their perspicuity outside the CONtext of apostolic teaching.
In particular, it is hard maintaining that 2 Peter is exactly a letter encouraging any approach to Scripture outside a sound guide.

,
3:15-16 “And consider the patience of our Lord as salvation, as our beloved brother Paul, according to the wisdom given to him, also wrote to you, speaking of these things as he does in all his letters. In them there are some things hard to understand that the ignorant and unstable distort to their own destruction, just as they do the other scriptures”
As for Psalm 119, it will be noted that it speaks about Law.
Now, since the Reformed position appears to be that perspicuity stands or fall on what is necessary ( to know, believe and observe ) for salvation, and since we are told by reformed brothers that any part of Mosaic Law is not exactly that, we can say that any text dealing about Law appears essentially irrelevant to the support of that position.
Since the very foundation of reformed soteriology is to be found in the pauline letters, we’ve just seen 2 Peter is not precisely a support for the Westminster Confession or similar statements
Scripture is profitable.“All Scripture is breathed out by God and profitable for teaching, for reproof, forcorrection, and for training in righteous-ness, that the man of God may be compe-tent, equipped for every good work” (2Tim 3:16-17).
That Scripture is profitable is manifestly irrelevant to the issue of the right context to get such a profit.
Scripture explains salvation.“. . . the sacred writings, which are able to make you wise for salvation through faithin Christ Jesus” (2 Tim 3:15b).
Again, it is undisputed that Scripture explains salvation.
Scripture is addressed to com-mon people, not religious ex-perts.“Hear, O Israel” (Deut 6:4).“The common people heard Him [Jesus]gladly” (Mark 12:37, NKJV).“to the saints who are in Ephesus” (Eph1:1).“with all those who in every place callupon the name of our Lord JesusChrist” (1 Cor 1:2).
On Deuteronomy, see the point above on Law .
As for pauline quotations, I wonder how the fact of an apostle writing to local churches he has founded and personally taught can support the position that Scripture can and has to be understood outside the context of the Apostolic Church.
The quotation from Mark is rather astonishing: the very words delivered by the Lord are seemingly confused with Scripture.

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Parents can teach Scripture to their children.“And these words that I command youtoday shall be on your heart. You shallteach them diligently to your children, andshall talk of them when you sit in yourhouse, and when you walk by the way, andwhen you lie down, and when you rise”(Deut 6:6-7).
See again above for the Law.
Even a child can understandScripture’s message.“But as for you, continue in what you havelearned and have firmly believed, knowingfrom whom you learned it and how fromchildhood you have been acquainted withthe sacred writings. . . ” (2 Tim 3:14-15a).
We just have here that Timothy has been taught the OT since he was a child.
Scripture tests the accuracy of religious ideas.“Now these Jews were more noble thanthose in Thessalonica; they received the word with all eagerness, examining theScriptures daily …" Acts 17*
The conclusions of other jewish believers knowing the same Scriptures were different. That looks rather a blow to the doctrine we are examining.
End of the quotation
I am aware some other pericopes can be quoted for an alleged support of perspicuity besides those found in that paper , and hope someone else ( hopefully a protestant brother ) can point to them too.
At this point the following question is nevertheless unescapable:
" Is the doctrine of the perspicuity of Scripture perspicuous in Scripture , and is this a necessary requisite or not for it ?"