Sun Imagery

Now that quatrain 1 has gotten us to see how time is like the sea, we get to compare it to the sun in quatrain 2. The question is, what does this new line imagery add to what we already know about the passage of time, or how does it change it? By comparing human life to the sun that gloriously rises up to be "crowned," only to be destroyed by evil eclipses, Shakespeare reveals a greatness in human life that goes beyond the mindless struggle towards death illustrated by the wave-imagery from quatrain 1, as if to say, hey, we all get it pretty good for a while. And then we croak.

• Lines 5-8: What we're dealing with here is a conceit in which the sun stands in for human life. This is different from the simile from Lines 1-4, where the comparison was made pretty stinkin' obvious through the words "Like" (Line 1) and "so" (Line 2). But in quatrain 2, the connection between life and the sun is never exactly spelled out. Instead, the connection develops gradually, from the vague hint in the phrase "main of light" (Line 5). The metaphor remains a bit hidden in Line 6, but then comes blazing to the forefront in the imagery of the "eclipses" "fight[ing]" against the new adult's "glory." Once this imagery is in place, we can then go back to Line 6 and see how that imagery of "crawl[ing] to maturity" and being "crowned" with it could be interpreted as the sun climbing up the sky to its highest point at noon. Don't worry if this seems a bit complicated: this sonnet, and this stanza especially, is notorious as being one of the most weirdest (in terms of its language) that Shakespeare ever wrote. 
• Lines 5-6: Okay, things are about to get a bit weirder. Our apologies if your mind gets a little bent out of whack by what we're about to say—but Shakespeare hasn't left us any choice. The weird thing here is Shakespeare's use of personification in talking about "Nativity." Doesn't "nativity" refer to human beings already? Well, yes, but it's an extremely abstract way of talking about people. So, what Shakespeare has really done is abstractify (yep, we totally made that word up) human life by referring to it generally as "Nativity," but then he takes that abstraction and re-personifies it, by making it perform various human actions, like "crawl[ing]," getting "crowned," and so on. Weird stuff. But so it goes. 
• Line 8: Wait, haven't we heard this one before? The entire line here is a bit of a cliché, taken from the Book of Job, verse 1:21. As Stephen Booth points out on page 240 of his commentary on the sonnets, this line from Job would have been especially familiar to people in Shakespeare's day because it was used in the traditional burial service. Only instead of having God as the subject of his sentence, Shakespeare gives all that power to time. When God is the one bringing things to light and laying them to waste, the process can be interpreted as part of a divine plan. If you're a believing Christian, this whole process even has a payoff: if you are good, you will be rewarded in the afterlife, in heaven. By talking about time instead of God, Shakespeare turns his back on all that. In the view of this sonnet, the destruction of everything that exists is meaningless, and there is no reward in the afterlife. Did Shakespeare genuinely believe this? We have no way of knowing. But the way this Sonnet uses this cliché seems far from pious.