The Taz (Yorah Deiah 251:6) writes, "Saving a life always comes first. [If a person has a choice whether to save a life or to study Torah, obviously, saving a life takes precedence.] Nothing stands in the way of pikuach nefesh. The Gemara is saying that the merit of learning Torah is greater than the merit of saving lives."
Shulchan Aruch (Yorah Deiah 245:5) states, "When does one begin teaching Torah to his son? When the child begins to speak, teach him to say יעקב קהילת מורשה משה לנו צוה תורה, and the first pasuk of Shema. Continue teaching him gradually until he reaches six or seven years old, and then bring him to a melamed." Because we want the child's first words that he hears and speaks to be words of Torah.
Learning Torah is the Greatest Mitzvah
It states (Mishlei 8:11), וכל מפנינים חכמה טובה כי בה ישוו לא חפצים, "For wisdom is better than pearls; all desirable things cannot compare to it." The Gemara (Moed Katan 8:) adds, חפצי אפילו בה ישוו לא שמים, "Even mitzvos don't compare to Torah." Because the greatest mitzvah a person can perform is to study Torah.
This is not the way people generally see things. If you ask unlearned people, "What is the greatest deed a person can do?" many will respond that saving a life is the greatest mitzvah. Indeed, saving a life is a great mitzvah, but Chazal (Megillah 16:) say, תלמוד גדול נפשות מהצלת יותר תורה, "Studying Torah is greater than saving lives."
The Gemara adds, "Studying Torah is greater than building the Beis HaMikdash... Studying Torah is greater than kibud av ve'eim."
Pirkei Avos (6:5) states, "Torah is greater than kehunah and meluchah (kingship)."
The Chofetz Chaim (Toras HaBayis ch.5) writes, "My friend, think about the precious value of each moment of Torah so that you won't waste your time. For example, imagine that you once had the merit of saving someone's life. Someone was drowning in the river, and you jumped in and saved him. How proud you would be! You will never forget that moment. For the rest of your life, you will talk about it. And, indeed, it is an incredibly great mitzvah to save a life. As Chazal say, 'Whoever saves a Yid's life, it is like he saved the entire world.' If you saved many lives, your joy will be boundless..."
The Chofetz Chaim continues, "One person saved lives, and another learned Torah. Each acted correctly, according to the situation they were in. If the question is raised, 'Who performed a greater mitzvah?' Everyone will say the person who saved lives performed a greater mitzvah! However, Chazal reveal that studying Torah is greater than saving lives... Although our eyes are covered, and we don’t recognize things this way, Chazal revealed this secret. The merit of studying Torah is extremely great. Nothing in the world compares to it. This is why Dovid HaMelech prayed so much for success in Torah (in Tehillim 119)."
The Gemara (Chagigah 5) says, “Hakadosh Baruch Hu cries for three groups of people each day." One of them is "Someone who has the ability to study Torah and doesn’t."
Why does Hashem cry for him?
The Chofetz Chaim explains that it is because Hashem is our father. Wouldn’t a father cry when he sees his son throwing away opportunities for attaining extreme wealth? Hashem also cries when He sees us wasting precious time that could have been used for amassing something more precious than gold and diamonds.
