What is the meaning of "Necheni v'Tzidkasecha"?
Radak: Help me to go in the path of Tzedakah and Mishpat, and guide me in it lest I stumble. This is a Tefilah that Hashem save him from mistakes and Mezid sins - "mi'Nistaros Nakeni; Gam mi'Zedim Chashoch Avdecha" (19:13-14).
Malbim: Show me the Kodesh path of Torah; it should not veer from my sight, lest my haters, who count my steps, rejoice [at my fall].
Who are "Shorerai"?
Rashi: My haters, who hope to see me betray You and You will abandon me. This is like "Ashurenu v'Lo Karov" (Bamidbar 24:17). Radak - they look for evil, like "va'Yhi Sha'ul Oyen Es David" (Shmuel I, 18:19).
Why did he say "ha'Yeshar Lefanai Darkecha"?
Malbim: A person errs either b'Shogeg, for he does not know the path, or even if he knows the path, due to hindrances or mountains. Make the path straight in front of me, before I go on it. The Nimshal is, sometimes the Torah path makes one err without knowing the good path, due to lack of understanding, the depth of the matter, and the many alternative paths. Therefore, he asks Hashem to teach him the ways of life (16:11). Sometimes things distract him from his way, due to seeking his essential needs and the leaning of desire towards excesses, like Moreh ha'Nevuchim says. Therefore he asks "make the path straight."
