As far as the first Question is concerned, you can see the diverse opinions of Interpreters concerning this matter enumerated both in POOLE’S Synopsi Criticorum, and in WOLF’S Curis philologicis et criticis, on this passage. Namely, various interpreters think that the supplement of the phrase, διὸ λέγει, wherefore he says, is to be fetched from the context, whether they reach back to Πνεῦμα, the Spirit, mentioned in verse 9, or to Κύριον, the Lord, in verse 10, or to Χριστὸν/Christ, at the end of this verse 14, which opinion of OEDER WOLF specifically calls in for examination: from whom, as you learn that this opinion last mentioned is to be indicated as undoubtedly harsher; so it is observed, that those that supply the text in the ways previously set forth thus interpret the same, that either, with the remaining things in this Epistle and in this context delivered by Paul, there is an imposition, as if those things did not so much proceed from the Holy Spirit; or the manner of speaking agrees more with the sermons of the Prophets, than with the writings of the Apostles and especially of Paul. To the word φῶς/light, which had immediately preceded, a number of learned Men more or less earnestly return: but who by the φῶς/light again in a diversity of ways understand either the Light of the Holy Spirit speaking and admonishing within the regenerated and illuminated man, or the Light of the Word or the ancient Scripture, which is a torch to the feet and a lamp to the path of the faithful, Psalm 119:105, or the man filled with Light, in comparison with verses 8 and 13. BEZA on this passage hesitantly sets forth this opinion: “He says, that is, Scripture, or God speaking through a Prophet, or even light itself by personification, just as in Hebrews 12:5, ἡ παράκλησις, the exhortation, is said διαλέγεσθαι, to reason with or speak to, us as children. Now, it appears that this was taken partly from Isaiah, etc.” GROTIUS with greater παῤῥησίᾳ/license embraces this exegesis: “Διὸ λέγει, wherefore that light, that is, the man filled with light says to another. Paul does not appear to me to adduce some passage, but to ascribe to the light, that is, to the man filled with light, words that are worthy of him.” Grotius is followed by JAKOB ELSNER, in his Observationibus Sacris, “Διὸ λέγει,” says he, “I understand with Grotius, φῶς/light, that is, the man filled with new light, verse 13, who is commanded ἐλέγχειν, to reprove, those ἔργα σκότους, works of darkness, verse 11, as φῶς/light and a child of the φωτὸς/light, verse 8, in such a way that the words here following contain a prescribed formula whereby one ought ἐλέγχειν, to reprove, wicked men and to call them back to the light.” The Most Illustrious JAN VAN DEN HONERT cites Grotius and Elsner and professes to stand in their footsteps, in his De voornamste heilige eu schrifftuurlyke Sinnebeelden, uit verscheidene oudheden opgeheldert, door wylen Arnoldus Ruiquig, on the word Opstaan/rise, tome 2, pages 1045-1048, as far as τὸ φῶς, the light, is introduced as speaking by personification: but he explains τὸ φῶς λέγον, the light speaking, of the Holy Spirit speaking not through testimony that He had taken care to be consigned to writing by holy Men; but through internal testimony in the heart of the regenerate man, who himself, now as made Light in the Lord, according to this convicting light of the Spirit, is held to refute, and to excite to duty, both himself and others; in which manner the twin signification of τοῦ φωτὸς, the Light, occurring together in verse 8, comes into consideration. I discover that the Most Illustrious PETRUS LAAN, in his Concionibus selectis, Sermon XVII, pages 303, 304, understood it of the Light of the Word speaking, which he thinks to have been understood by the Apostle immediately before in verse 13 by τὸ φῶς, the light. Unless these learned Men had held it as certain that the following words read in verse 14 are nowhere found in any certain place of the Old Testament codex, and are not borrowed from there; I believe that most of them would not have stooped so easily unto this opinion. Now, the Apostle is not accustomed by this, διὸ λέγει, wherefore he says, or a similar formula, in express words to introduce either the Holy Spirit speaking, unless he is reciting His words read in the Old Testament, or even a man filled with the Light of the illuminating and sanctifying Spirit. Where any defect of speech is perceived, indeed it appears that it is to be supplied most suitably from the immediate context: but that in the case of the formula of which the Apostle here makes use, λέγει, he says, or διὸ λέγει, wherefore he says, is not always able to be done so conveniently. For example, in Ephesians 4:8 we also have διὸ λέγει, wherefore he says: it would be most nearly at hand to accommodate this declaration τῷ Χριστῷ, to Christ, of whom the Apostle had just made mention in verse 7, teaching, ἑνὶ δὲ ἑκάστῳ ἡμῶν ἐδόθη ἡ χάρις κατὰ τὸ μέτρον τῆς δωρεᾶς τοῦ Χριστοῦ, unto every one of us is given grace according to the measure of the gift of Christ. It immediately follows in verse 8, διὸ λέγει, wherefore he says. However, what words are cited in verse 8 out of Psalm 68:18 are not composed in such a way that in them we are able to propose to ourselves Christ the Lord speaking in particular; since, on the other hand, in them the speech is made either to Christ according to the construction of the Hebrew text, or concerning Christ according to the form of the words in the Pauline citation. Now, the more reluctantly I consent in understanding under the verb λέγει, he says, in our text the noun φωτὸς/light, the more difficultly is the signification of the noun φωτὸς/light in the immediately preceding verse 13 determined; yet to what is more attention to be paid than to the more remote verse 8, when the name of φωτὸς/light is not ever repeated in our text, but is supplied from the immediate context. For by no means beyond controversy is it posited, whether τὸ φῶς, the light, in verse 13, occurring twice, once in each hemistich, comes in one and the same sense, or in diverse senses, the first metaphorical, the next proper, or in more than one metaphorical sense. Therefore also, because neither is it certain, whether τὸ φανερούμενον is to be taken actively or passively; whether φῶς/light is to be taken as the subject or the predicate of the latter clause; whether πᾶν/all/whatsoever is to be construed with τὸ φανερούμενον in the nominative; whether indeed πᾶν/all/ whatsoever in the accusative case is to be supposed to be the object, concerning which the action expressed by τὸ φανερούμενον belongs. Hence the manifest divergence of opinions among Theologians in the explanation of that verse; some of which, for example, consider the latter words, πᾶν γὰρ τὸ φανερούμενον φῶς ἐστί, as a common saying, by which the native force of natural Light is indicated, for the confirmation of that which the Apostle had already said concerning metaphorical Light: or they believe whatever works of darkness are thus made manifest throught the refutation of spiritual Light are thus indicated, so that they might be set in clear light. Others through that entire verse discuss either the Light of the Spirit shining within and the man filled with this light; or the Light of the Word declaring all things and also shining within the regenerate man; or the Light of the divine omniscience and providence; or even the final Judgment or the light of the last day, on which the universal Judgment shall be help by the Lord, in which every works shall be brought into the light, with all that is hidden, whether good or bad, comparing Ecclesiastes 12:14; 1 Corinthians 3:13: although WOLF taxes this opinion in OEDER, who certainly incorrectly draw the argument of verse 14 here, as if he would refer the word by which Christ on the last day is going to compel the dead in their Resurrection, properly so called, to appear before His tribunal; yet I see that the same with respect to the sense of verse 13 has approved itself also to the Most Learned MARTIN, certainly not an Interpreter of the least rand, writing on this passage in his notis Gallicis ad Biblia Sacra, after other things having regard to this also, which had been set down before on the prior part of the verse: “[Because the light] The light of the last day. [It is that manifests all] It will be that which will manifest all the actions of men, Romans 2:16, so that the present tense is put many times in this text in the place of the future, as in verse 6, and often elsewhere”: with whom compare also DIODATI in his notis Gallicis on verses 13 and 14.
 Matthew Poole (1624-1679) was an English, Noncomformist Presbyterian Pastor, Theologian, and Exegete. Having been ejected from the ministry by the Act of Uniformity (1662), he undertook the compilation of his massive and masterly Synopsis Criticorum, a verse-by-verse history of interpretation. Poole’s Synopsis was tremendously influential in the work of Matthew Henry and Jonathan Edwards.
 Petrus Laan (1696-1743) was Professor of Theology at Franeker from 1738 to 1743.
 Ephesians 5:13: “But all things that are reproved are made manifest by the light: for whatsoever doth make manifest is light (τὰ δὲ πάντα ἐλεγχόμενα ὑπὸ τοῦ φωτὸς φανεροῦται· πᾶν γὰρ τὸ φανερούμενον φῶς ἐστί).”