רמב"ן — והאלהים נסה / כי עתה ידעתי

Q — How can Hashem 'test' Avraham if He already knows the outcome? And what does 'עתה ידעתי' mean — did Hashem just now learn something?

A — Ramban's foundational teaching on nisayon: the test is for the one tested, not the tester. Hashem already knew Avraham's potential יראת ה'; the akeida brings that יראה 'מן הכח אל הפועל' — from latent capacity to realized deed. The reward differs: 'שכר מעשה טוב' is greater than 'שכר לב טוב בלבד'. Hashem tests only tzadikim whom He knows will succeed, never the wicked, and 'כל הנסיונות שבתורה לטובת המנוסה'. 'עתה ידעתי' is דברה תורה כלשון בני אדם — what was previously known only to בוחן לבבות is now known publicly through action. The shevua at the end (which Ramban distinguishes from earlier merely conditional promises) seals the brachot as unconditional — 'הבטחה שלימה בגאולה העתידה לנו'.