Significance of Devotional Service
Without devotional service, all other methods for spiritual self-realization are weak and insignificant. Unless one comes to the devotional service of Lord Krishna, jnana yoga cannot give the desired results.
Obtaining Liberation
Speculative knowledge alone, without devotional service, is not able to give liberation. On the other hand, even without knowldege one can obtain liberation if one engages in the Lord’s devotional service. — Sri Chaitanya Caritamrita, Madhya Lila, 22.21.
Real Result of Devotional Service
The real result of devotional service is the awakening of pure love for the Supreme Personality of Godhead, which continues under all circumstances.
Srimad Bhagavatam 5.24.19,
Srila Prabhupada
Understanding The Supreme Lord
One can understand the Supreme Personality as He is only by devotional service and when he is in full consciousness of the Supreme Lord by such devotion, he can enter into the kingdom of God. — Bhagavad Gita, 18.55.
Capturing Lord Krishna
If one wants to capture Him, one must undertake devotional service.
Srimad Bhagavatam 10.9.10,
Srila Prabhupada.
Starting of Devotional Service
Devotional Service should start at early age, and not during old age.