Why does the Torah write "Ashom Asham la'Shem"?
Rashi (according to Mizrachi, from Toras Kohanim): To teach us that the ram of Asham Shifchah Charufah must also be worth two Shekalim.
Targum Yonasan: To teach us that whoever is Chayav a Korban Asham is obligated to bring it as an Asham in the Name of Hashem (to atone) for the sin that he performed. 1
Moshav Zekenim (6): Even though he brings the Korban due to Safek, it is an Asham (a Korban for great guilt; it is an Asham to Hashem, who knows all hidden matters, and if he sinned, He would punish him (if he did not offer the Korban to shield him).
See Na'ar Yonasan.
Why does it write "Asham Hu"?
Rashi: To teach us that the Asham Nazir and the Asham Metzora do not need to be worth two Shekalim.
Seforno: Even though it sometimes happens that he brings the Korban and in fact did not sin, he should not worry about having brought Chulin into the Azarah, 1 since the Korban comes (not for the actual sin, but) for not having taken care not to enter into a Safek. 2