What is Guru Ji Ki Sewa

Please write your comments and your understanding
"What is meaning of Guru Ji Ki Sewa"

I personally think that Guru Ji Ki Sewa means Waheguru Ji De Naam Da Simran Hai (Naam Japna = Guru Ji Ki Sewa)

Sahib Shri Guru Granth Sahib Ji
Ang -223 (Guru Nanak Dev Ji)
Guru Ki Sewa Shabad Vicchar

Sukhmani Sahib - Ang 265
Jan Rataa Har Naam Ki Sewa
and later
Sant Ki Sewa Naam Dhiyaaeai

Guru Arjan Dev Ji - Ang 375
Har Sewa Mukh Amrit Naam

Guru Amar Das Ji - Ang 426
Naamai Ki Sabh Sewa Karai, Gurumukh Naam Bhujhaee

Guru Nanak Dev Ji - Ang 905
Dhur Ki Sewa Raam Raveejai

Guru Arjan Dev Ji Says Ang 741
"Guru Ji Ki Sewa Karoo Din Raat " - What kind of sewa you can do day and night, I think, Guru Ji is saying Do Simran Day and Night.