The interpretation timeline
Psalm 118:1 Douay-Rheims

ALEPH. Blessed are the undefiled in the way, who walk in the law of the Lord.

A.D. 373 – 1875 6 witnesses

Patristic

before A.D. 750
373
A.D.
c. A.D. 296–373
“And as he is Firstborn among brothers and rose from the dead "the firstfruits of them that slept"; so, since it became him "in all things to have the preeminence," therefore he is created "a beginning of ways," that we, walking along it and entering through him who says, "I am the Way" and "the Door" and partaking of the knowledge of the Father, may also hear the words, "Blessed are the undefiled in the Way," and "Blessed are the pure in heart, for they shall see God."”
Source
430
A.D.
Augustine of Hippo Patristic
A.D. 354–430
“From its commencement, dearly beloved, doth this great Psalm exhort us unto bliss, which there is no one who desireth not. ...And therefore this is the lesson which he teacheth, who saith, "Blessed are those that are undefiled in the way, who walk in the law of the Lord" (ver. 1). As much as to say, I know what thou wishest, thou art seeking bliss: if then thou wouldest be blessed, be undefiled. For the former all desire, the latter fear: yet without it what all wish cannot be attained. But where will any one be undefiled, save in the way? In what way, save in the law of the Lord? ...”
Source
523
A.D.
c. A.D. 450–523
“And again, in another place, he [David] ascribeth blessedness to the man who feareth God, and he maketh known what good things the fear of God worketh in him that feareth [Him], saying, "Blessed is the man that feareth the Lord", and here the fearer of God is accounted blessed. And although our Lord ordained blessings for other things, the prophet David accounted blessed the fearer of the Lord. "Blessed is the man who hath not walked in the way of the wicked", and it is well known that he walketh not in the way of the wicked because he feareth God. And again he saith, "Blessed is the man whom Thou shalt correct, O Lord, and whom Thou shalt teach Thy law", and it is manifest that the fear of God teacheth the laws, and that the man who feareth confesseth his correction. And again he said, "Blessed are those who are without blemish in the way, and who walk in the law of the Lord", and here again the fear of the Lord preserveth [a man] from blemishes, and urgeth him to walk in the way of the law. And again he saith, "Blessed is the man whose iniquity is forgiven, and whose sins are covered", and it is well known that here also the fear of God bringeth to repentance, through which the forgiveness of sins is given, and through the suffering and tears which are produced by the fear of God the form of a man's sins is covered before his eyes. And again he saith, "Blessed is every one that feareth the Lord, and who walketh in His ways", and here again the prophet David sheweth that a man walketh in the way of the commandments through the fear of God. And in another place he saith concerning him that feareth the Lord, "He taketh heed to the commandments which are given by the Lord."”
Source

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“ALEPH.--The First Part. ALEPH. Blessed are the undefiled in the way,.... Who are in the right way to heaven and happiness, which is Jesus Christ; the strait gate, and narrow way to eternal life; the only true way of life and salvation, in which way believers walk by faith. All out of this way are altogether become filthy; but all in this way are clean, even every bit: they are without spot and blemish, blameless and unreproveable, and without fault, before the throne of God and in his sight; being washed from their sins in the blood of the Lamb, and clothed with his righteousness; and even "perfect" and complete in him, as the Targum renders the word. These are also found in the way of their duty, and walk in all the commandments and ordinances of the Lord, blameless before men, and are sincere and upright in the sight of God; and are upon all accounts happy persons: who walk in the law of the Lord: within the boundaries and limits of it, according to its direction, as it is a rule of walk and conversation in the hands of Christ the Lawgiver; and who continue to walk in it, as in a pleasant path, with great delight; and cheerfully obey its precepts, as influenced by the love of God, and assisted by the Spirit and grace of Christ. The word "law", or "doctrine", as it signifies, may design every revelation of the divine will; and even the doctrine of Christ, which believers should abide in, and not transgress; and should walk uprightly according to the truth of it, and as becomes it, and as they are enabled to do.”
Source
1849
A.D.
1774–1849
“Alleluia. There is no title in Hebrew. But (Haydock) this psalm contains the praises of the Lord, and of his holy law, under fourteen different names, (Worthington) of way, testimony, &c., repeated in every verse, except the 122d, (Muis) with surprising variety, so as to avoid tautology, and to give a most perfect system of moral doctrine. It is written according to the order of the Hebrew alphabet, (Haydock) that we may learn it from our infancy. (St. Hilary) — Eight verses begin with each of the twenty-two letters. St. Jerome (ad Paulam Urb. & Proem. in Lam.) moralizes on the signification of these letters, which he renders, 1. Aleph, &c., “the doctrine— 2. of the house; 3. the plenitude, 4. of the tables (or holy scriptures )— 5. This 6. and 7. this 8. of life— 9. a good 10. beginning— 11. the hand 12. of discipline (or the heart)— 13. From them 14. everlasting 15. help— 16. the fountain (or eye) 17. of the mouth 18. of justice— 19. the calling 20. of the head 21. of teeth 22. the signs.” By thus connecting the letters, he forms sentences to shew that the holy Scriptures bring us to the knowledge of the Church, and of Christ, &c. See Worthington. Thus every thing serves to excite the devotion of the saints, though the proud may deride their ingenuity. The sacred writers have certainly found some pleasure and utility in writing so frequently in the alphabetical order, though we may not perceive the advantages of it. (Haydock) — David is supposed to have written this psalm for the instruction of Solomon in his youth, (Berthier) though others believe that he composed it while he himself was young, and persecuted by Saul. (Muis; Bossuet, &c.) — It seems very probable, that Daniel wrote it for the consolation of the captives. (Calmet) (Daniel ix. 2.) — Origen and Ven. Bede refer it to those times; though it seems in reality to appertain to all who desire to live piously, (Haydock) and it is only a conjecture that any other but David was the author, to whom it is generally attributed. Its excellency cannot be denied, and the Church has adopted it for her daily office, dividing it into eleven psalms. (Berthier) — St. Augustine has written thirty-two, and St. Ambrose twenty-two sermons on the contents; and St. Basil observes, that David has here comprised in one psalm the sum of all that he has written in the rest. Among other points of morality and doctrine, we may remark, that the psalmist insists on the necessity of God’s grace, and the co-operation of free will, (Worthington) and overturns the Protestant system of justification. (Du Hamel) — The Israelites might recite this psalm on their journey, three times a-year, to the temple, as the fifteen gradual canticles which follow, were to be sung on the steps leading to the house of God. (Bellarmine) (Menochius) — Lord. Such only are happy here, (Worthington) or hereafter. (Haydock) — All aim at happiness, but only the virtuous take the proper means to attain it. (St. Augustine) — The way may here designate this life, (Worthington) or the law, (St. Augustine) or Jesus Christ, John xiv. 6. (St. Ambrose) The psalmist evidently presupposes, that some can and do keep the law. (Worthington)”
Source
1875
A.D.
Keil & Delitzsch Lutheran
1861–1875
“The eightfold Aleph. Blessed are those who act according to the word of God; the poet wishes to be one of these. The alphabetical Psalm on the largest scale begins appropriately, not merely with a simple (Psa 112:1), but with a twofold ashr. It refers principally to those integri viae (vitae). In Psa 119:3 the description of those who are accounted blessed is carried further. Perfects,a s denoting that which is habitual, alternate with futures used as presents. In Psa 119:4 לשׁמר expresses the purpose of the enjoining, as in Psa 119:5 the goal of the directing. אחלי (whence אחלי, Kg2 5:3) is compounded of אח (vid., supra, p. 273) and לי (לוי), and consequently signifies o si. On יכּנוּ cf. Pro 4:26 (lxx κατευθυνθείησαν). The retrospective אז is expanded anew in Psa 119:6: then, when I namely. "Judgment of Thy righteousness" are the decisions concerning right and wrong which give expression to and put in execution the righteousness of God. (Note: The word "judgments" of our English authorized version is retained in the text as being the most convenient word; it must, however, be borne in mind that in this Psalm it belongs to the "chain of synonyms," and does not mean God's acts of judgment, its more usual meaning in the Old Testament Scriptures, but is used as defined above, and is the equivalent here of the German Rechte, not Gerichte. - Tr.) בּלמדי refers to Scripture in comparison with history.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.