यथा दीपो निवातस्थो नेङ्गते सोपमा स्मृता। योगिनो यतचित्तस्य युञ्जतो योगमात्मनः ॥

yathā dīpo nivāta-stho neṅgate sopamā smṛitā yogino yata-chittasya yuñjato yogam ātmanaḥ

As a lamp in a windless place flickereth not, to such is likened the Yogî of subdued thought, absorbed in the yoga of the Self.

In plain words: Krishna says the mind of a yogi deep in meditation is like a lamp flame in a place with no wind. It does not flicker.