"From that time Jesus began to show to His disciples that He must go to Jerusalem, and suffer many things from the elders and chief priests and scribes, and be killed, and be raised the third day. Then Peter took Him aside and began to rebuke Him, saying, Far be it from You, Lord; this shall not happen to You! But He turned and said to Peter, Get behind Me, Satan! You are an offense to Me, for you are not mindful of the things of God, but the things of men. Then Jesus said to His disciples, If anyone desires to come after Me, let him deny himself, and take up his cross, and follow Me... For the Son of Man will come in the glory of His Father with His angels, and then He will reward [apodidomi] each according to his works [praxis]" (Matthew 16:21-27).
The Greek word praxis means 'action', 'act', 'conduct', 'practice'. The best definition is found in the epistle to the Romans, "For if you live according to the flesh, you will die; but if by the Spirit you put to death the works [praxis] of the flesh, you will live. For all those who are led by the Spirit of God, those are sons of God" (Romans 8:13-14 Darby). 'Praxis' is related to the old man, "Having put away the old man and his works [praxis]" (Colossians 3:9 Darby). When Jesus explained to His disciples that He had to go and die in Jerusalem, Peter reacted with his own mind, that of the old nature, which was not yet renewed.
Peter opposed God's plan, that is why Jesus said to him, "Get behind Me, Satan…". In fact, he who opposes God is a satan, that is to say an adversary. Jesus then said to His disciples, "If you want to follow Me, that is to say walk in the purposes of God, you must renounce your old man, that is to say crucify him, to be able to follow Me". Our thoughts are at the origin of our acts, of our actions and our behaviour. We are called to carry out the works [ergon] of God prepared in advance for us (Ephesians 2:10). But to accomplish these works of faith we must rid ourselves of the old man and his works [praxis].
The Greek verb apodidomi means 'to render', 'to give back to some one a thing which belongs to him', 'to pay what is due', 'to reward'. We must understand that our acts [praxis] are like sowing, and we will reap what we have sown (Galatians 6:7-8). When Jesus comes, what we have sown will then be given back to us as what is due, and, in this passage, for example, we see that it is a question of evil things since they come forth from our old nature. In the Kingdom of God, there is no room for the flesh and its works. And, because of our old nature and the acts it produces, we can lead our soul to eternal ruin (Matthew 16:26). That is why Jesus asks us to crucify our SELF every day in order to follow Him to accomplish the true works of God on the earth.