Matthew 19:27 - Ellicott's Commentary On The Whole Bible

Behold, we have forsaken. — The question betrayed the thoughts that had been working in the minds of the disciples, and of which, as was his wont, St. Peter made himself the spokesman. They had complied with their Master’s commands. What were they to have as the special reward to which they were thus entitled? It is obvious that in asking for that reward they showed that they had complied with the letter only, not with the spirit, of the command. They had not in the true sense of the word, denied themselves, though they had forsaken the earthly calling and the comforts of their home; and they were dwelling on what they had done, as in itself giving them a right to compensation.