“I have surely visited you.” When God “visited” someone, He intervened in their life, and He could intervene for the better or for the worse. The exact meaning of the Hebrew perfect tense of the verb here in Exodus 3:16 has been debated, and it could be a perfect of intent (“I have decided to intervene”), an instantaneous perfect (“I will now intervene”), or prophetic perfect (“I will intervene in the future”). However, it seems best given the situation that the perfect tense should be taken as literally meaning that God had already, in the past, started the process of delivering the Israelites from Egypt, which indeed He had, and in fact, had already foreseen that Egypt would have to be smitten for that to happen (cp. Exod. 3:20). No doubt the Israelites, who wanted to be free from their slavery in Egypt, remembered that Joseph had prophesied that God would visit Israel and bring them from Egypt to the Promised Land (Gen. 50:24-25).
[For more on “visit,” see commentary on Exodus 20:5.]