The speaker of the poem, presumably John Milton, is lamenting the passage of time. Specifically the problem is that the speaker feels that he has accomplished very little in his 23 years of life. He says that the days have flown by but he has nothing to show for it. "But my late spring no bud or blossom shew'th." He has entered manhood with almost nothing to show for it and is unsure of what his course should be.
The speaker's solution to that problem is to leave it in God's hands.The speaker knows that he has talents and whether or not he has a lot of time or a little time left on Earth, he wants to use that time to use his talents in a way that pleases God. "Time leads me, and the will of Heav'n [God]:/All is, if I have grace to use it so/As ever in my great Task-Master's [God's] eye. The solution makes sense because the author is John Milton who frequently wrote about God and religious topics.