Here are some of the views that we find in the commentaries. He was old but still able to walk. He went through the camp from tribe to tribe to show that their well-being still mattered to him. He went to bid farewell to every Israelite and to receive their farewell blessing. He aroused himself to carry out his task.
The people knew his days were numbered and didn’t want to worry him with anything extra but he insisted that he was still in office until the very last minute.
Or perhaps “he went” does not necessarily mean that he actually went anywhere on his own two feet but it is an idiomatic expression meaning that he – metaphorically – proceeded to what comes next in the verse, in this case to address the people. An analogy is Ex. 2:1 where a member of the tribe of Levi went and married a Levite woman.
However, whichever explanation we adopt, the result is more or less the same – Moses was active and alert until his very last moment.
It’s good to think of this as we approach the Day of Judgment. If only we could all be similarly blessed! We say in the prayers, “Cast us not off in time of old age” (Psalm 71:0). What a blessing it is to retain one’s energies to the end…