Genesis 1, being the first chapter, and of the first book of the Scripture, it is the foundation for all that comes after, it being the 'seed' of the whole of Scripture. The literal is the foundation, for all that which will come after, which will include things as parables, metaphors, symbols, and so on.
All of the other Texts of Scripture are based in its very beginning texts and pages. Please note, that this is not a new understanding, even as others have already stated themselves:
Thomas Aquinas, in Summa Theologica, Question 74, Article 3, Reply to Objection 6 and 7 - www . newadvent . org/summa/1074 . htm :
"...for all the senses are founded on one the literal from which alone can any argument be drawn..."
"... nothing necessary to faith is contained under the spiritual sense which is not elsewhere put forward by the Scripture in its literal sense. ..."
Further, we read:
[Thomas Aquinas begins this section by rebutting and refuting Augustine's position]
"...by the "evening" and the "morning" ... But, according to Basil (Hom. ii in Hexaem.), the entire period takes its name, as is customary, from its more important part, the day. And instance of this is found in the words of Jacob, "The days of my pilgrimage," where night is not mentioned at all. But the evening and the morning are mentioned as being the ends of the day, since day begins with morning and ends with evening, or because evening denotes the beginning of night, and morning the beginning of day. It seems fitting, also, that where the first distinction of creatures is described, divisions of time should be denoted only by what marks their beginning. And the reason for mentioning the evening first is that as the evening ends the day, which begins with the light, the termination of the light at evening precedes the termination of the darkness, which ends with the morning. But Chrysostom's explanation is that thereby it is intended to show that the natural day does not end with the evening, but with the morning (Hom. v in Gen.). ...
Reply to Objection 7. The words "one day" are used when day is first instituted, to denote that one day is made up of twenty-four hours. Hence, by mentioning "one," the measure of a natural day is fixed. Another reason may be to signify that a day is completed by the return of the sun to the point from which it commenced its course. And yet another, because at the completion of a week of seven days, the first day returns..."
Further Thomas states, in "Second Part of the Second Part "; "Question 122. The precepts of justice"; "Article 4. Whether the third precept of the decalogue, concerning the hallowing of the Sabbath, is fittingly expressed? - www . newadvent . org/summa/3122 . htm , speaking of the 7th Day, the Sabbath of the LORD thy God and the 'change' made to it by Catholicism:
"I answer that, ...Now the precepts of the decalogue are, so to speak, first and common principles of the Law, and consequently the third precept of the decalogue describes the exterior worship of God as the sign of a universal boon that concerns all. This universal boonwas the work of the Creation of the world, from which work God is stated to have rested on the seventh day: and sign of this we are commanded to keep holy seventh day--that is, to set it aside as a day to be given to God. Hence after the precept about the hallowing of the Sabbath the reason for it is given: "For in six days the Lordmadeheaven and earth . . . and rested on the seventh day." ..."
"...Reply to Objection 4. In the New Law the observance of the Lord's day took the placeof the observance of the Sabbath, not by virtue of the preceptbut by the institution of the Churchand the custom of Christian people...."
All of which is carried the further by their own support of Thomas Aquinas:
"The Summa Theologica of St. Thomas Aquinas
Second and Revised Edition, 1920
Literally translated by Fathers of the English Dominican Province
Online Edition Copyright © 2008 by Kevin Knight
Nihil Obstat. F. Innocentius Apap, O.P., S.T.M., Censor. Theol.
Imprimatur. Edus. Canonicus Surmont, Vicarius Generalis. Westmonasterii.
APPROBATIO ORDINIS
Nihil Obstat. F. Raphael Moss, O.P., S.T.L. and F. Leo Moore, O.P., S.T.L.
Imprimatur. F. Beda Jarrett, O.P., S.T.L., A.M., Prior Provincialis Angliæ
MARIÆ IMMACULATÆ - SEDI SAPIENTIÆ"