Solomon relates his personal experience Eccl. 2; the result of which was "no profit," and a conviction that all, even God's gifts of earthly good to good men, in this life are subject to vanity. His trial of God's first gift, wisdom, is recounted in Ecclesiastes 1:12-18.
Was - This tense does not imply that Solomon had ceased to be king when the word was written. See the introduction to Ecclesiastes. He begins with the time of his accession to the throne, when the gifts of wisdom and riches were especially promised to him 1-Kings 3:12-13.

I the Preacher was king - This is a strange verse, and does not admit of an easy solution. It is literally, "I, Choheleth, have been king over Israel, in Jerusalem." This book, as we have already seen, has been conjectured by some to have been written about the time that Ptolemy Philadelphus formed his great library at Alexandria, about two hundred and eighty-five years before our Lard; and from the multitude of Jews that dwelt there, and resorted to that city for the sake of commerce, it was said there was an Israel in Alexandria. See the introduction.
It has also been conjectured from this, that if the book were written by Solomon, it was intended to be a posthumous publication. "I that was king, still continue to preach and instruct you." Those who suppose the book to have been written after Solomon's fall, think that he speaks thus through humility. "I was once worthy of the name of king: but I fell into all evil; and, though recovered, I am no longer worthy of the name." I am afraid this is not solid.

(h) I the Preacher was king over Israel in Jerusalem.
(h) He proves that if any could have attained happiness in this world by labour and study, he should have obtained it, because he had gifts and aids from God to it above all others.

I the preacher was king over Israel in Jerusalem. Solomon having given a general proof of the vanity of all things here below, and of the insufficiency of them to make men happy, proceeds to particular instances, and begins with human wisdom and knowledge, which of all things might be thought to be most conducive to true happiness; and yet it falls short of it: he instances in himself for proof of it; and he could not have pitched on anyone more proper and pertinent to the purpose, who had all the advantages of obtaining wisdom, was assiduous in his pursuit of it, and made a proficiency in it above all mankind; wherefore he must be owned to be a proper judge, and whatever is concluded by him may be taken for granted as certain; and this is the sum of the following verses to the end of the chapter. Now let it be observed, that he was a "preacher", not a private person, and must have a good share of knowledge to qualify him for teaching and instructing others; and, more than this, he was a king, and did not want money to purchase books, and procure masters to instruct him in all the branches of literature; and when he entered upon the more profound study of wisdom, and especially when he said this, it was not in his infancy or childhood, or before he came to the throne, but after; even after he had asked, wisdom of God to govern, and it had been given him; yea, after he had been a long time king, as he now was; though the Jewish writers, as the Targum, Jarchi, and others, conclude from hence that he was not now a king, but become a private person, deposed or driven from his throne, which does not appear: moreover, he was king of Israel, not over a barbarous people, where darkness and ignorance reigned, but over a "wise and understanding people", as they are called Deuteronomy 4:6; and he was king over them in Jerusalem too, the metropolis of the nation; there he had his royal palace, where were not only the temple, the place of divine worship, but a college of prophets, and a multitude of priests, and an abundance of wise and knowing men, whom he had opportunity of conversing with frequently; to which may be added, his large correspondence abroad; persons from all kings and kingdoms came to hear his wisdom, as the queen of Sheba; and by putting questions to him, and so exercising his talents, not a little contributed to the improvement of them. Now a person so qualified must be a judge of wisdom, and what he says deserves attention; and it may be observed, that what he says, as follows, is "in verbo regis et sacerdotis", on the word of a king and preacher, who would never risk his honour, or forfeit his character, by saying an untruth.

Solomon tried all things, and found them vanity. He found his searches after knowledge weariness, not only to the flesh, but to the mind. The more he saw of the works done under the sun, the more he saw their vanity; and the sight often vexed his spirit. He could neither gain that satisfaction to himself, nor do that good to others, which he expected. Even the pursuit of knowledge and wisdom discovered man's wickedness and misery; so that the more he knew, the more he saw cause to lament and mourn. Let us learn to hate and fear sin, the cause of all this vanity and misery; to value Christ; to seek rest in the knowledge, love, and service of the Saviour.

Resumption of Ecclesiastes 1:1, the intermediate verses being the introductory statement of his thesis. Therefore, "the Preacher" (Koheleth) is repeated.
was king--instead of "am," because he is about to give the results of his past experience during his long reign.
in Jerusalem--specified, as opposed to David, who reigned both in Hebron and Jerusalem; whereas Solomon reigned only in Jerusalem. "King of Israel in Jerusalem," implies that he reigned over Israel and Judah combined; whereas David, at Hebron, reigned only over Judah, and not, until he was settled in Jerusalem, over both Israel and Judah.

"I, Koheleth, have been king over Israel in Jerusalem." That of the two possible interpretations of הייתי, "I have become" and "I have been," not the former (Grtz), but the latter, is to be here adopted, has been already shown. We translate better by "I have been" - for the verb here used is a pure perfect - than by "I was" (Ew., Elst., Hengst., Zck.), with which Bullock (Speaker's Comm., vol. IV, 1873) compares the expression Quand j'tois roi ! which was often used by Louis XIV towards the end of his life. But here the expression is not a cry of complaint, like the "fuimus Troes," but a simple historical statement, by which the Preacher of the vanity of all earthly things here introduces himself, - it is Solomon, resuscitated by the author of the book, who here looks back on his life as king. "Israel" is the whole of Israel, and points to a period before the division of the kingdom; a king over Judah alone would not so describe himself. Instead of "king על (over) Israel," the old form of the language uses frequently simply "king of Israel," although also the former expression is sometimes found; cf. 1-Samuel 15:26; 2-Samuel 19:23; 1-Kings 11:37. He has been king, - king over a great, peaceful, united people; king in Jerusalem, the celebrated, populous, highly-cultivated city, - and thus placed on an elevation having the widest survey, and having at his disposal whatever can make a man happy; endowed, in particular, with all the means of gaining knowledge, which accorded with the disposition of his heart searching after wisdom (cf. 1-Kings 3:9-11; 1-Kings 5:9).
But in his search after worldly knowledge he found no satisfaction.

I was king - Having asserted the vanity of all things in the general, he now comes to prove his assertion in those particulars wherein men commonly seek, and with greatest probability expect to find, true happiness. He begins with secular wisdom. And to shew how competent a judge he was of this matter, he lays down this character, That he was the preacher, which implies eminent knowledge; and a king, who therefore had all imaginable opportunities and advantages for the attainment of happiness, and particularly for the getting of wisdom, by consulting all sorts of books and men, by trying all manner of experiments; and no ordinary king, but king over Israel, God's own people, a wise and an happy people, whose king he was by God's special appointment and furnished by God, with singular wisdom for that great trust; and whose abode was in Jerusalem where were the house of God and the most wise and learned of the priests attending upon it, and the seats of justice, and colleges or assemblies of the wisest men of their nation. All these concurring in him, which rarely do in any other men, make the argument drawn from his experience more convincing.