Sforno on Deuteronomy 6:5/ספורנו על דברים ו׳:ה׳

1ואהבת, you will then enjoy doing things which are pleasing to Him when you understand that there is nothing in this world which is more worth doing. [the word ואהבת is not perceived a commandment by the author; in fact it is questionable if loving someone could be the subject of a commandment altogether. Ed.]