The Frost beheads it at its play— [...] The blonde Assassin passes on— (3-5)
Notice the words "beheads" and "Assassin" here. The connotations of neither one of those words are very nice, right? "Beheads" makes us think of a blood-drenched scene from the French Revolution (or Jeffrey Dahmer), while "Assassin" makes us think of some gun for hire with mad ninja skills. Both words are negative and put gruesome images in our heads. The diction deliberately shows death in the worst possible light. Is the speaker pointing an accusing finger at God? Perhaps.
In accidental power— (4)
We're backtracking a bit here, but we couldn't pass up this line. It needs its moment in the sun. So here's a question: if God made everything, then how can the deathly power of the frost be "accidental?" Is the poem saying that God isn't the all-powerful creator? If that's the case, then maybe he's no more to blame for all this than anybody else.
For an Approving God. (8)
The last line is the kicker. After taking us though this whole thing about happy flowers dying at that hands of a cold-blooded killer, we're told that God thinks this is a-okay. What's the moral of the story here? God is a sadistic killer? Death is a part of God's plan, so we ought to stop fretting about it? Maybe there's no moral at all. It could be that the poem is just saying, "This is how it is, folks. Roll with it."