1)
Why will he thank Hashem "Me'od"?
1.
Malbim: One who is saved from evil thanks only for the salvation, but not for the evil; it would have been better if there was no evil, and he would not have needed salvation. However, since the evil was a reason for the good, I will thank greatly, also for the evil.
2)
Why will he praise Hashem "b'Soch Rabim"?
1.
Radak: It is so they will know that my salvation was via Him, and they will increase their trust in Him.
2.
Malbim: So many will know that He caused [the evil and salvation], and fathom His praise.
