The highest service of all is to Jap Naam. It is true that Naam will only reside in the heart when we serve Vaheguru with devotion and love, but how do we get to the point of devotion and love?
Naam residing in the Hirda is the same thing as having Vaheguru's Charan Kamal Parkaash in our Hirda. These are different terms that describe the same thing. The only way to get to this point where Naam resides in the Hirda is to do non-stop Abhiyaas-Kamayee of Naam. The continuous recitation of Naam using the Gurmat Vidhi will eventually result in the Parkaash of Naam within our Hirda, or in other words, Jot Da Parkaash.
The devotional service of Vaheguru is following all of Guru Sahib's Hukams. We must keep Rehit, read Bani, and Jap Naam. Results are in the hands of Vaheguru.
Preetam Singh