What does Matthew 25:42 mean?
The first group addressed by Jesus (Matthew 25:31–33), the righteous, elect believers (Ephesians 4:1; Matthew 24:22; Mark 13:27; Romans 11:7; Titus 1:1), followed Him faithfully, meeting the needs of those who were suffering, especially other believers. In doing so, they were serving Jesus Himself (Matthew 25:34–40).The rest—the second group called "goats"— failed to give Him food or drink when He was hungry and thirsty. In fact, as the following verses show, they failed to care for Him when He suffered all the various needs met by those called the sheep. The sins Jesus holds these unbelievers accountable for are sins of neglect (Matthew 25:43–46).
It's important to note that the actions Jesus describes here are not what cause these people to be approved or condemned (Titus 3:5). Rather, they are demonstrations of their faith in Him (John 13:31–35, 14:15). Those who show no love for believers are not, themselves, really believers (1 John 4:20).