Recommended only because of its historical significance, the Lectures on Faith are the “doctrine” part of the Doctrine and Covenants as it was first published in 1835. The lectures were later excised, by the RLDS Church in 1897 and by the LDS Church in 1921, the latter citing the fact that the lectures had never been officially sustained by the general church membership as reason for its expulsion. (It probably didn’t help that, by the time the lectures were removed, the non-corporeal God promoted in the lectures no longer jived with Mormon teachings on the nature of the Godhead.)
From a 21st-century perspective, even an LDS one, the lectures are outdated. There is little in the way of profound theology here. Many teachings are vague—perhaps even inconsistent—and often rely on a literal view of scripture that modern readers may have difficulty accepting. The particular edition I read also features an appendix filled with quotes by various church leaders, past and present, the apparent purpose of which is to promote a post-correlation interpretation of the primary text. For example, when God the Father is referred to as a “personage of spirit,” an asterisk informs you to turn to the appendix, where we learn that “the phrase ‘personage of spirit’ simply means that God has a resurrected body of flesh and bone, quickened by the Spirit” (p. 78). If that’s not convincing enough for you, maybe the quotes from Bruce R. McConkie will help. There are several of those, too.