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.
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,
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.
Devotional Service should start at early age, and not during old age.