When a person does a mitzvah, they are melding the past, present, and future, and this is very apparent in this mitzvah. Sforno says on this, that the word hanofel, fallen one, implies a person who falls is morally liable. We cannot simply rely on Hashem for saving someone we put in a dangerous situation, or if we put ourselves in a dangerous situation, but Sforno says that, even if someone was not to follow this mitzvah, their death would still have been ordained. This mitzvah is juxtaposed by the mitzvah of shooing away the mother bird, for which Hashem promises us a long life.
Interestingly enough, the Talmud tells a story about a person falling while completing the mitzvah of shooing away the mother bird.
The Talmud's conclusion here is similar, that one cannot rely on a miracle in the case where one has put oneself in a dangerous situation. Similarly, we have faith in Hashem but put a fence around our roofs.
In establishing something new, we have three mitzvot that orient us in the past, present, and future. We keep part of our house unfinished, reminding us of the destruction of the Temple and our mourning for the Temple. We place mezuzahs, reminding us of our obligation to fulfill the commandments and Hashem's protection of our houses. And we build a fence, to avoid future tragedy by negligence.
Similarly, the mitzvah of bikkurim requires us to think of the past, present, and future. We even talk of these in our words - we acknowledge where we come from, our avot, and the connection they and our ancestors had with Hashem that led to the existence of the Jewish people. We acknowledge the love Hashem had for us to take us out of Egypt. We acknowledge our current state of having done the mitzvah to the extent of the law, and we celebrate in the mitzvah we are doing. And we acknowledge our faith in Hashem's role to bless us in the future and to keep faith with us.
The blessings, and curses require us too, to think of the past, present, and future. The curses in Ki Tavo are often mentioned, but not much attention is often paid to the blessings. The blessings are mentioned first and are almost the exact opposite of the first curses. For everything that looks bad in the world, the world has the opportunity to be just as good (and even better) than it looks in our worst days. For every darkness we experience, the light we can experience if we do teshuva and follow Hashem can be just as bright.
The curses in Vayikra have words of comfort for us at the end. The curses in Devarim do not. One explanation I've heard for why this is is that Hashem's mercy is greater than that of any human. Another explanation is that Hashem's faith in us doing teshuva is greater than any human's faith in other humans doing teshuva. As humans, we know we will sin, and often it looks bleak for the condition of humanity. We trust Hashem will keep faith with us, but Hashem knows we will do teshuva, because he sees everything and knows everything, and has perfect faith in us. Therefore, he is able to give us comfort that we are both capable of and will do teshuva, which Moshe as a human (even as the holiest human who ever lived) could not provide.
These parashot deal heavily with the concepts of past, present, and future, and our own role on them, through the concepts of protecting ourselves and others from danger in the future rather than simply relying on miracles, the words said during the bringing of bikkurim and what they mean for the past, present, and future, and the future blessings and curses that we incur by following or not following Hashem's laws.