First of all, NEVER say, “well if HE doesn’t have to keep the mitzvah, so why do I??” Never say that, no matter who it is. Never compare your level of shomer torah u’mitzvos with someone elses. Your motivating factor should be a rock-solid foundation of Emunah, together with a live Rebbi who you can speak to. You must keep the torah and mitzvos because you are a jew, period. Never mind the next fellow, even if he’s a “Yaakov Avinu”.
The Telzer rav z”l explains, the way the Avos kept the torah was different from us since it was before Matan Torah. The way they did mitzvos was bechinas Rofeh LeCholeh- in the spirit like that of a doctor to a patient. The doctor tells a patient not to smoke, for example, the patient can listen or ignore. It is no doubt good advice and probably the right way to go. However the patient ultimately can choose not to listen, especially if he has his own cheshbonos. The avos kept the torah because they knew it was the right way to live. However if there were certain times they felt necessary to do something opposite of what the torah says, they did so with the greatest of intentions and with ruach hakodesh.