What is "Bisarti Tzedek"?
Rashi: [We sang] Shiras ha'Yam, Shiras ha'Be'er, Shiras Devorah 1 .
Radak: I must do one matter in addition to fulfilling the Mitzvos - to tell the Chasadim that You did for me. I told them "b'Kahal Rav", so many will hear and thank Your name. Besorah is usually good news, but it can be bad - "va'Ya'an ha'Mevaser" (Shmuel I, 4:17).
Only Devorah and Barak sang that Shirah! Even so, it is attributed to all of Yisrael, for it was due to their salvation. (PF)
Why did he say "Sefasai Lo Echleh"?
Rashi, Radak: I will not stop [my lips from telling Your Tzedakah]. This is like "va'Yikalei ha'Geshem" (Bereishis 8:2), "Lo Sichleh Rachamecha" (verse 12).
Malbim: Do not think that I tell the miracle that You did for me amidst pride, as if I want to boast that I was virtuous, and therefore Hashem helped me. It is proper for Shelemim (people who perfected themselves) to hide their virtue and not glorify themselves in front of many. That shows that their virtue was not l'Shem Hashem, rather, to boast! I need not withhold my lips [from telling Your Nes for me], for You know that I do not intend to boast.
Why did he say "Hashem Atah Yadata"?
Radak: What my lips tell, many know. What my heart thinks about Your Tzedakah, You know, and no one else.
Malbim: Refer to 40:10:2:2.
