Discuss the theme of John Milton's sonnet "How Soon Hath Time"?

I think the biggest theme of this excellent sonnet is the
way that the world looks on achievement and expect visible signs of having achieved
something or done something with our lives, whereas actually this sonnet argues that
"achievement" and "growth" can result from internal and intellectual
pursuits.

If we have a closer look at the wording of this
sonnet, it begins with a recognition of how quickly time flies and how the speaker has
already passed his twenty-third year:

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How soon hath time, the subtle thief of
youth,

Stolen on his wing my three and twentieth
year!

However, what concerns
the speaker above all is the way in which in his "late spring" there is no evidence of
having achieved or done something with his life: "no bud nor blossom sheweth."
Nevertheless, the speaker argues that he has achieved "inward ripeness" in spite of the
lack of evidence that he can point towards to suggest that he has been engaged in
meaningful pursuits. The poem ends with a statement of belief in a God who has a perfect
plan for each stage of our lives and can see both the inner "ripeness" and the
outer:

All is,
if I have grace to use it so,
As ever in my great taskmaster's
eye.

Thus this poem is really
about our lives and what we do with them. Whether we have accomplished tangible exploits
that others can look to or not, this poem argues that we must not neglect our own
"inner" maturity and that we should have confidence in God's plan for our lives rather
than our own plan or the plans of others for us.