Why did he say "Ken Avarechecha b'Chayai"?
Rashi: This is like Az Avarechecha b'Chayai; the Targum of "Az" (Shemos 15:1) is b'Chen. Then, when I will come in front of You, I will bless You all the days of my life.
Radak: Like I praise You the entire 1 day, so I will bless and praise You my entire life.
Malbim: So is the Brachah that I bless You in my lifetime. I do not bless You for life, rather, for the Chesed that I can praise You.
This Mizmor did not mention that David praises Hashem the entire day. Perhaps it should say 'today'. However, I did not see any texts of Radak like this. (PF)
Why does it say "b'Shimcha Esa Kapai"?
Rashi: [I lift my hands] to pray and to praise [Your name].
Radak: With Your help I lift my hands against those who combat me. This is like "b'Shimcha Navus Kameinu" (44:6) - with Your help, i.e. I will call Your name. This is like "ha'Melamed Yadai la'Kerav" (144:1).
Malbim: I do not pray for physical life and worldly needs, only for Your name - that I can thank and bless Your name.
