Christianity

There's no doubt that our speaker is Christian, and is deeply concerned with questions stemming from Christian theology. The Christian belief in the Garden of Eden and Christ's resurrection shape the way our speaker perceives the world, and the poem can largely be read as a prayer (an emotionally complex one, at that), beginning with praise, turning to a plea and source of concern, and finally acknowledging God's dominion.

• Line 8: The "racing lambs" are an image that is part of the scene our speaker is giving us. They contribute a sense of youthfulness, playfulness, and joy; I mean, come on, they are little baby sheep, running around! They are also (probably because of how cute and playful they are) a pretty widely recognized symbol of innocence. They help confirm how we are to view this scene of spring, and prepare us for the reference to the biblical Garden of Eden (the time before sin, when all was innocent).
• Lines 10-11: The story of Adam and Eve is the first explicit biblical allusion we get in the poem. And not only does alluding to this story help us understand how our speaker sees the spring scene he's been describing, but it also sets us up for what's to come. Because the allusion to Eden calls to mind the whole story, including original sin and the expulsion from Eden, we are prepared for the upcoming focus on sin. So we see that this allusion to Eden helps our speaker convey a lot in a pretty small space – a definite plus when you are writing a sonnet (and generally a good idea in any poem).
• Lines 11-12: When our speaker addresses Christ, we can definitely think of this poem as a prayer. A prayer, though, is essentially an apostrophe, since our speaker is addressing an abstract being.
• Lines 11-12: We also get a bit of anaphora, when our speaker repeats the phrase "before it" in two successive clauses. It's not only pleasing to the ear, but it helps get across the emotional state of our speaker. We hear him repeating this plea to Christ, and only slightly revising the word he uses to describe the ruining of the innocent mind. The fact that he lingers on it tells us that he's fairly obsessed and concerned. He's also speaking so urgently that sometimes he gets a little ahead of himself and has to go back to get the right word.