Christ relates the Parable of the Fig Tree (verses 29-33) to give instruction regarding His warnings in the previous verses. The "these things" in verse 31 refers to the question asked in verse 7 and Jesus' subsequent answer in verses 8-28. "These things" are the events foretold to happen as the end nears. In the parable, Christ provides the perspective we should have as we anticipate the unfolding of the previously described events.
What owner of a fig tree would spend hours each day scrutinizing his tree to see if it was budding? Would he make the fig tree the focal point of his day? Of course, no one would. An owner of a fig tree would be aware of its location, its level of health, and its progression through the annual cycle of growth, but these matters would not require his all-consuming effort.
The parable, then, shows us that we should be aware of prophecy, we should keep an eye on what is happening in the world, but it does not require—and we should not allow it to become—our primary focus. In the fig-tree analogy, Jesus illustrates for us the balanced view we should have toward prophecy. We must be aware of what is taking place, but we need not be over-attentive.
Some make the mistake—a spiritually dangerous mistake—of ignoring the lesson of this parable by making prophecy a major or even sole focus that distracts them from their primary spiritual responsibilities. It is easier to focus on prophecy and world events than it is to give the same scrutiny to the evils lurking in our corrupt human nature (Jeremiah 17:9). In Luke 21, Christ definitely does not overlook the latter, as we see in verses 34-35:
But take heed to yourselves, lest your hearts be weighed down with carousing, drunkenness, and cares of this life, and that Day come on you unexpectedly. For it will come as a snare on all those who dwell on the face of the whole earth.
With the opening "But" in verse 34, Christ's message takes a definite turn. He is still talking about preparing us for the end of the age, but He shifts from the external events of verses 7-33 to the internal: "take heed to yourselves, lest your hearts. . . ." He is no longer talking about world events, the physical and external, but our "hearts," the spiritual and internal. He gives a warning to those who are not spiritually aware and focused—those who are distracted. They will be caught completely off guard—"that Day come[s on them] unexpectedly"—because their hearts are misdirected.
Verse 35 re-emphasizes that the end will be a surprise to some people, one that Christ compares to a bird snared or trapped. Why? Verse 34 supplies the reason: They are burdened by the "cares of this life," not focused on what counts. They are looking in the wrong direction, and the trap springs on them without warning. Rather than overcoming the world (I John 5:4), as Laodiceans, they are being absorbed by it (Revelation 3:14-22).
Between verses 8-33 and verses 34-35 of Luke 21, we can also see a contrast in the awareness levels we need to have regarding the physical versus the spiritual. For the physical, we are to be aware but not over-attentive. For the spiritual, however, Christ raises the level of vigilance: "Take heed to yourselves," or be on guard! He exhorts us to be in a high state of spiritual alertness.