Sforno on Deuteronomy 26:16/ספורנו על דברים כ״ו:ט״ז

1היום הזה, that You entered into the covenant with him. The “covenant” comprised the undertaking by Israel to keep G’d’s statutes as something that would ensure their welfare, something He had not done for any other nation.

2בכל לבבך, you must embrace these laws with all your heart, without mental reservations or doubts about their authenticity. Your sole motivation must be to carry out His will.

3ובכל נפשך, you must not allow yourself to be distracted, sidetracked, by the evil urge, i.e. temptations, because you are so firm in the belief of the superiority of the Lawgiver.