I am not sure I can make it any more clear.
Maybe you should define what you mean by “basis for assurance”. What is the basis for your basis?
The light of Faith is a gift, much like the light of the natural reason is a gift. God made us in His IMAGE and LIKENESS, which means we have the ability to know and to love. That is, He instilled in us the first principles of our natural knowledge, without them we would be lost, being unable to abstract any universals from our experiences. We would have no ability to acquire scientific knowledge of any sort. In like manner, without the gift of Faith, we have no ability to advance in the divine science. Without first principles there can be no science. Even when we encounter a rule of Faith, like the Sacred Scriptures, lovingly compiled for us, or miracles, or the teachings of the Early Church Fathers, or teachings of the Bishop of Rome, both ordinary and extraordinary, it is our Faith which resonates when presented with Truth, it is the work of the Holy Spirit in our souls, and it is a beautiful thing. But the gift of Faith comes, not as a single virtue, no, Faith comes in a trinity of virtue, for with Faith comes also Hope and Charity. It is impossible to study the science of God, as known through revelation, without Charity.
I have explained this to you before, and all you want to do is to respond with "The light of Faith is a gift," which is a given, but ignores the instrumentality of that, in which faith has some degree of warrant."
Saving faith is in the "Man whom he hath ordained; whereof he hath given assurance [pistis] unto all men, in that he hath raised him from the dead.
Whereof he hath given assurance (pistin paraschōn). Second aorist active participle of parechō, old verb to furnish, used regularly by Demosthenes for bringing forward evidence. Note this old use of pistis as conviction or ground of confidence (Heb_11:1) like a note or title-deed, a conviction resting on solid basis of fact. All the other uses of pistis grow out of this one from peithō, to persuade. - WORD PICTURES IN THE NEW TESTAMENT by Archibald Thomas Robertson
"And Elijah took the child, and brought him down out of the chamber into the house, and delivered him unto his mother: and Elijah said, See, thy son liveth." "And the woman said to Elijah, Now by this I know that thou art a man of God, and that the word of the Lord in thy mouth is truth." (1 Kings 17:23-24)
"Now are we sure that thou knowest all things, and needest not that any man should ask thee: by this we believe that thou camest forth from God." (John 16:30)
"But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name." (John 20:31)
My assurance is based upon Scriptural substantiation in word and in power, with Scripture being Divine based upon its unique Heavenly qualities and attestation, and then what i believe being in conformity of with that assured wholly Divinely inspired word of God, both in text and in effects, and which includes that which is seen in history and personal testimony.
However, the basic premise of Rome is that since this allows for and see different conclusions, then determination and assurance of Truth cannot be gained by personally objectively examining evidences in the light of Scripture, which the RC is not to do in order to ascertain the veracity of RC teaching, and instead an assuredly infallible magisterium is essential, and which the magisterium Rome is, and thus it is upon the premise of her assured veracity that one has assurance of Truth.
As Cardinal Avery Dulles stated: People cannot discover the contents of revelation by their unaided powers of reason and observation. They have to be told by people who have received in from on high. Even the most qualified scholars who have access to the Bible and the ancient historical sources fall into serious disagreements about matters of belief.” - Cardinal Avery Dulles, SJ, “Magisterium: Teacher and Guardian of the Faith,” p. 72; http://triablogue.blogspot.com/2008/08/magisterial-cat-and-mouse-game.html
Thus an assuredly infallible magisterium is held as being essential for knowing both which revelation and writings are of God and their meaning, and it is then argued that Rome is that magisterium in the light of her historical descent.
But which effectively nukes the church as the church actually began in dissent from those who sat in the seat of Moses over Israel, who were the historical instruments and stewards of Scripture, and inheritors of promises of Divine guidance, presence and perpetuation.
And instead they followed an itinerant prophet in the desert, and then an itinerant Preacher whom the magisterium rejected, and whom the Messiah reproved by Scripture, with it being supreme, (Mk. 7:2-16) and established His Truth claims upon scriptural substantiation in word and in power, as did the early church as it began upon this basis. (Mt. 22:23-45; Lk. 24:27,44; Jn. 5:36,39; Acts 2:14-35; 4:33; 5:12; 15:6-21;17:2,11; 18:28; 28:23; Rm. 15:19; 2Cor. 12:12, etc.)
What this means is that an assuredly infallible magisterium is not essential for determination and assurance of Truth, and for providing and preserving it, but assurance of Truth is based upon Scriptural substantiation, with Scripture being the transcendent supreme standard for obedience and testing and establishing truth claims as the wholly Divinely inspired and assured, Word of God, which it is abundantly evidenced to be.
And which testifies (Lk. 24:27,44, etc.) to writings of God being recognized and established as being so (essentially due to their unique and enduring heavenly qualities and attestation), and thus they materially provide for a canon of Scripture (as well as for reason, the church, etc.)
The magisterium is to authoritatively confirm both men and writings of God as being so, but not as possessing infallibility, and such are of God regardless of the rejection of the magisterium. And thus the church began, with the veracity of the magisterium being itself dependent upon Scriptural substantiation, and not as superior to Scripture which Rome makes herself to be.
For not only does she presume to uniquely determine what is of God and their meaning, but the veracity of RC teaching is not dependent upon the weight of Scriptural substantiation, but upon the presumed veracity of Rome. Under which premise all is made to conform to her.
For Rome has presumed to infallibly declare she is and will be perpetually infallible whenever she speaks in accordance with her infallibly defined (scope and subject-based) formula, which renders her declaration that she is infallible, to be infallible, as well as all else she accordingly declares.
It was the charge of the Reformers that the Catholic doctrines were not primitive, and their pretension was to revert to antiquity. But the appeal to antiquity is both a treason and a heresy. It is a treason because it rejects the Divine voice of the Church at this hour, and a heresy because it denies that voice to be Divine...The only Divine evidence to us of what was primitive is the witness and voice of the Church at this hour. — "Most Rev." Dr. Henry Edward Cardinal Manning, "Lord Archbishop" of Westminster, The Temporal Mission of the Holy Ghost: Or Reason and Revelation (New York: J.P. Kenedy & Sons, originally written 1865, reprinted with no date), pp. 227-228.
>Catholic doctrine, as authoritatively proposed by the Church, should be held as the supreme law; for, seeing that the same God is the author both of the Sacred Books and of the doctrine committed to the Church, it is clearly impossible that any teaching can by legitimate means be extracted from the former, which shall in any respect be at variance with the latter. Hence it follows that all interpretation is foolish and false which either makes the sacred writers disagree one with another, or is opposed to the doctrine of the Church.(Providentissimus Deus; http://www.vatican.va/holy_father/leo_xiii/encyclicals/documents/hf_l