Revelation21:17

1: “By the human measurement, that is also the angel’s measurement.”

This explanatory statement is added because, as humans, we often have a different perspective than that of God and His angels. However, if we are living a pure life, our perspective is much more likely to be similar to that of heaven. The point being made here is that God protects and does so very well. While we play a part in our own protection by not allowing certain things into our minds, God is the one primarily responsible for protecting us and He does a perfect job of it (12 times 12). The only perspective which claims that God does not protect us is the self-centered perspective of one who hopes to never suffer, never feel pain, never be inconvenienced, and never have to exert effort.

Why did the vision bother to explain that the angel’s measurement was the same as the human measurement? It is likely that a reader would think of Ezekiel’s vision of the temple in which the angel was using a different cubit than the one that was common in Ezekiel’s time. There were several differently sized cubits used in ancient times ranging from 17 inches (44 cm) to over 20 inches (52 cm). I recommend you go to this site to read more about it:

https://answersingenesis.org/noahs-ark/how-long-was-the-original-cubit/

It appears that the earlier cubits were the longest ones and as time went by the cubits became shorter. For the building of the temple Solomon (presumably by God’s command) used an old cubit which was longer than the one in use at his time, possibly the old Hebrew cubit known as the Hebrew long cubit which was 20.4 inches (51.8 cm) in length. By the time of Ezekiel’s vision the length of the cubit being used by the angel was described as a cubit and a hand breath (Ez 43:13). When Jesus gave John this vision, He knew that John and his readers might want to know if this was their cubit or a longer cubit as had been the case with Ezekiel’s vision.

However, the answer may not refer at all to measuring physical things. I think the answer was an indication that we have been given enough information to measure our own lives (not someone else’s life) and have an idea of how God will “measure” us. It was about measuring spiritual things, not physical things.