Are there degrees of punishment and rewards after the judgment?
In II Peter 2:20-21 Peter states, "For if after they have escaped the pollutions of the world through the knowledge of the Lord and Savior Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning. For it had been better for them not to have known the way of righteousness, than, after they have known [it], to turn from the holy commandment delivered unto them."
Could this mean that the person will receive a harsher punishment than those that refused to obey the gospel?
In regards to reward, in II John 1:8, John states, "Look to yourselves, that we lose not those things which we have wrought, but that we receive a full reward."
What does full reward mean? Are there people that will receive a greater reward?
People who believe that there is one equal reward for all who are saved generally go to the parable of the workers in the vineyard in Matthew 20:1-16. Each set of laborers is hired at different times of the day, but in the end, each is paid the same amount. "But he answered one of them and said, 'Friend, I am doing you no wrong. Did you not agree with me for a denarius? Take what is yours and go your way. I wish to give to this last man the same as to you. Is it not lawful for me to do what I wish with my own things? Or is your eye evil because I am good?'" (Matthew 20:13-15). In this parable, I believe that the pay offered is eternal life, something that is offered to all faithful followers. "And he who reaps receives wages, and gathers fruit for eternal life, that both he who sows and he who reaps may rejoice together" (John 4:36). The length of one's service to the Lord does not impact the reward received.
However, there are other passages that also must be considered. In the parable of the talents (Luke 19:12-27), servants were given a set amount of funds to invest while the master was gone. One was able to take one mina and produced 10 more from it. And the master told him, "Well done, good servant; because you were faithful in a very little, have authority over ten cities" (Luke 19:17). Another servant produced 5 more minas and was told, "You also be over five cities" (Luke 19:19). Thus it appears that while all faithful followers are given eternal life as a reward, in that eternal life we will have different responsibilities or roles based on our productivity for the Lord here. It is an application of a principle stated earlier by the Lord, "He who is faithful in what is least is faithful also in much; and he who is unjust in what is least is unjust also in much" (Luke 16:10).
One person can measure the character of another by observing how he does with small things. If a person is willing to steal small things because "it doesn't matter" then you can be sure that given the opportunity he'll steal larger things as well. If someone is trustworthy enough to pay you back a dollar that he owes you will be reliable with larger sums as well. That is why eternal life is said to be determined by seemingly small things. "Then the King will say to those on His right hand, 'Come, you blessed of My Father, inherit the kingdom prepared for you from the foundation of the world: for I was hungry and you gave Me food; I was thirsty and you gave Me drink; I was a stranger and you took Me in; I was naked and you clothed Me; I was sick and you visited Me; I was in prison and you came to Me.' Then the righteous will answer Him, saying, 'Lord, when did we see You hungry and feed You, or thirsty and give You drink? When did we see You a stranger and take You in, or naked and clothe You? Or when did we see You sick, or in prison, and come to You?' And the King will answer and say to them, 'Assuredly, I say to you, inasmuch as you did it to one of the least of these My brethren, you did it to Me" (Matthew 25:34-40).
Another passage to consider is "For the Son of Man will come in the glory of His Father with His angels, and then He will reward each according to his works" (Matthew 16:27). One way to read this passage is that each person will get either eternal life or eternal punishment based on what he has done. But it is also possible that Jesus is saying Christians will each be rewarded in proportion to what they have done.
A more obscure passage is Paul's discussion of each man's works. "For no other foundation can anyone lay than that which is laid, which is Jesus Christ. Now if anyone builds on this foundation with gold, silver, precious stones, wood, hay, straw, each one's work will become clear; for the Day will declare it, because it will be revealed by fire; and the fire will test each one's work, of what sort it is. If anyone's work which he has built on it endures, he will receive a reward. If anyone's work is burned, he will suffer loss; but he himself will be saved, yet so as through fire" (I Corinthians 3:11-15). In the context, Paul describes himself as a master builder and those he has converted as the material being built up into a temple for God. Seen in this way, the success of those Paul converts to Christ are a benefit and joy to Paul when they too reach heaven. "For what is our hope, or joy, or crown of rejoicing? Is it not even you in the presence of our Lord Jesus Christ at His coming? For you are our glory and joy" (I Thessalonians 2:19-20). The opposite would also be true. If someone you worked with and converted does not make it, you'll suffer loss, though you yourself should make it.
I think this is what John had in mind when he said, "For many deceivers have gone out into the world who do not confess Jesus Christ as coming in the flesh. This is a deceiver and an antichrist. Look to yourselves, that we do not lose those things we worked for, but that we may receive a full reward" (II John 7-8). It is clear he is not talking about losing his own reward, but since he is concerned about others, whom he has worked with, he is expressing a desire to see them in heaven that his joy may be as full as it can be.
In regards to punishment, there also seems to be degrees of punishment. In the parable of the servants, Jesus said, "And that servant who knew his master's will, and did not prepare himself or do according to his will, shall be beaten with many stripes. But he who did not know, yet committed things deserving of stripes, shall be beaten with few. For everyone to whom much is given, from him much will be required; and to whom much has been committed, of him they will ask the more" (Luke 12:47-48). Related to this is the warning in Hebrews 10:28-29, "Anyone who has rejected Moses' law dies without mercy on the testimony of two or three witnesses. Of how much worse punishment, do you suppose, will he be thought worthy who has trampled the Son of God underfoot, counted the blood of the covenant by which he was sanctified a common thing, and insulted the Spirit of grace?"