The selection of the Israelites and their redemption from Egypt were not driven by physical might or vast numbers. Instead, these pivotal events were built upon two deep spiritual foundations: an inner bond of love and a historical promise. The primary approach among commentators is that God did not choose the people because of their size, but rather entirely out of His profound love for them [רש״י, ביאור שטיינזלץ].
The commentators present intertwining views on the exact nature of this love. One approach links it to the spiritual readiness of the people. While God loves all His creations, the Israelites received a special love because they are the descendants of those who truly loved God and focused on His name [ספורנו]. Their pure souls, drawing strength from the roots of the holy forefathers, are more prepared than other nations to connect intimately with the Divine [ביאור יש״ר]. Conversely, another perspective emphasizes that this love does not depend on intellectual greatness. Rather, it is a natural, unexplainable bond, much like a father's love for his son, arising from the idea that the soul of Israel is a piece of the Divine from above [העמק דבר, מלבי״ם]. If God had merely desired a massive population, He could have easily chosen the Egyptians and left the Israelites to merge with them into one giant nation. However, God is not interested in impurities, but rather in the pure and unique fruit [מלבי״ם, שפתי כהן].
The second foundation for the redemption is the fulfillment of a historical promise. God acted because He kept the oath He swore to the forefathers [מזרחי, שפתי חכמים, גור אריה, רש״י, אבן עזרא]. This oath was intended to designate the Israelites as His chosen people, to rest His presence upon them in a land uniquely prepared for that purpose, and to completely uproot the mentality of slavery from their souls [העמק דבר, מלבי״ם]. This promise carries an eternal guarantee: because of the oath, even if the people sin and face punishment, God will never completely cast them away [ביאור יש״ר].
These two foundations, the love and the oath, perfectly complement one another. The oath alone would not have been enough to bring the Israelites out of Egypt at that specific moment, as the four hundred years of slavery originally decreed to the forefathers had not yet passed. Therefore, it was only the powerful combination of the binding oath and God's immense love that caused Him to step in, redeem the people [ביאור שטיינזלץ], and save them much earlier than expected [שפתי כהן].