“witnesses against you.” The heavens and earth were not witnesses in a trial that very day, but rather that the heavens and earth were called to hear what God had done for Israel and to be willing to be witnesses against Israel should they ever accuse God of not giving them choice between life and death and encouraging them to choose life. In Ezekiel 33:11 God declares that He does not have any pleasure when wicked people die, and he urges the wicked to turn from their evil ways and live. On the Day of Judgment there will surely be some wicked people who are facing annihilation in the Lake of Fire who will accuse God of never giving them the choice to live forever.
The heavens and the earth will be around forever in one state or another, so they are a good witness for God—they won’t be absent on the day of the trial. Furthermore, God speaks to them about what He does (Deut. 32:1; Isa. 1:2) and says to the people that the heavens and earth will be His witnesses against them (Deut. 4:26; 30:19; 31:28). Moreover, the very nature of the heavens and earth point to a creator. There is more and more evidence for intelligent design in the creation around us, and Romans 1:20 says that God’s power and divine nature can be understood from what He has made. That, combined with the innate ability that mankind has to know good from evil (Gen. 3:22), means that a person should know to find God and then obey Him. If a person chooses to ignore God, that is his choice and God will honor that choice, but it is a poor choice and will result in the person’s death.
The idea that inanimate things that would be around for a long time could be witnesses to an oath was common in the culture and occurs at different times in the Bible (cp. Gen. 31:52; Josh. 24:27; Micah 6:2).
[For more on annihilation in the Lake of Fire, see Appendix 5, “Annihilation in the Lake of Fire”].
“choose life so that you may live—you and your seed—.” This is very similar to Deuteronomy 30:15-16 in that Deuteronomy 30:19-20 are one sentence and God asks each person to “choose life,” which we do by living a godly lifestyle and obeying God. Note that the sentence reads, “choose life so that you may live—you and your seed—by loving Yahweh your God, by obeying his voice and by holding fast to him.” God tells us exactly how to live a successful life here and now and have everlasting life later: love God, obey God, hold fast to God.