Vaishnava Samhita. Gopinatha Charitam. Vol II Book VI Chp 6 Shloka 8

यस्य सन्दर्शनादेव कृष्णभक्तिः प्रजायते |
स एवाचार्यवर्यो हि दीक्षया किं फलं ततः  ||

He whose very darshan sows the seeds of Krishna bhakit, is the greatest guru. What is the use of preaching or imparting knowledge through deeksha etc?