1)
What are "Sar'apai"?
1.
Radak: They are my thoughts about the length of Galus.
2.
Malbim: They are my thoughts and investigations of matters of conduct ]of the world] and serenity of Resha'im.
2)
What is the meaning of "Tanchumecha Yesha'ash'u"?
1.
Radak: Consolations written in the Nevi'im, they delight my Nefesh, for I know that they will not be false.