דברי הימים א, פרק ט״ז, פסוק י״ט

The promise to inherit the land of Canaan was given under circumstances that highlight a profound sense of wonder and divine kindness. Reflecting back on the days of the Patriarchs [רד״ק, מצודת דוד], this early family consisted of a small, limited group of individuals who could easily be counted [מצודת ציון, מצודת דוד, ביאור שטיינזלץ]. The land was not granted to them because of military strength or a large population. Instead, the promise was made precisely when they were few in number and physically weak [רש״י, ביאור שטיינזלץ].

Their vulnerable situation was further shaped by their social standing. The Patriarchs were not permanent residents of the land; they lived there simply as strangers [מצודת דוד, ביאור שטיינזלץ]. If God had promised this inheritance to a settled nation, or even to people with the secure status of permanent residents, it would not be particularly surprising. The true power and unique nature of His oath stem from the fact that He made this promise to the Patriarchs when they were just a few individuals living in a temporary, insecure state as mere outsiders [רש״י].