John 17:19-20

John 17:19-20. And for their sakes I sanctify myself that they also might be sanctified through the truth. Neither pray I for these alone, but for them also which shall believe on me through their word;

Christ knew that his Church would grow. He did not merely pray for the little handful of disciples who were with him there, but he preyed for all who, in after years, should believe on him.