“Then he said to them all, “If any want to become my followers, let them deny themselves and take up their cross daily and follow me. 24 For those who want to save their life will lose it, and those who lose their life for my sake will save it. 25 What does it profit them if they gain the whole world, but lose or forfeit themselves? 26 Those who are ashamed of me and of my words, of them the Son of Man will be ashamed when he comes in his glory and the glory of the Father and of the holy angels.” (Lk 9:23-26).
The prior verses are part of the passage. If you say that you do not know Christ, out of shame for being a Christian, then Christ will say He does not know you. It’s stating the obvious: if I claim NOT to be a Christian, simply because I am too ashamed to admit it, then how could I truly be a Christian?