bound together, they are still viewed as two things. "Cleaving to G*d," however, is so strong a form of unification that they are not two separate entities - they are truly one.
We thus understand that the same act - extending a loan for example - when performed with the intent of "cleaving to G*d" is infinitely greater than the same act performed as a separate mitzvah; the latter lacks total loss of self and only attains attachment - not cleaving - to G*d.
This also explains why the verse states "cleave to Him." Although this requires "cleaving to His ways," no action is specified, for the intent here is not to speak of the act itself - "His ways" - but the result of the act; when one is so at one with G*d, following in His ways will come as a matter of course.
Thus it is told of the Alter Rebbe that on Fridays towards evening he would automatically fall asleep, since it was then a time of sleep Above. i.e., his cleaving to G*d was so intense that the proper actions - "ways" - followed spontaneously.
Acting in such an unprompted and unpremeditated manner in consonance with G*d's desires reveals the tremendous degree of innate cleaving that a Jewish soul has to G*d. When the Torah commands us to "cleave to G*d," it empowers all of us to reveal our latent qualities.