"Blessed are the merciful: for they shall obtain mercy. Blessed are the pure in heart: for they shall see God. Blessed are the peacemakers: for they shall be called the children of God." (Matthew 5:7-9)

All of the descriptions of the elect child of God given by Jesus are evidences of the Spirit of God already dwelling inside the person. The three attributes listed in these verses are some of the clearest evidences of active grace in a person's life. 

A person who is merciful cares for the poor conditions of others. They act just like Christ Who found us in a miserable condition and showed mercy and compassion on us. Only those who have the Spirit of God in them can exhibit the nature of God. Therefore, a merciful person has the Spirit of God now and will receive eternal mercy. 

The natural heart of a man is deceitful above all and desperately wicked (Jeremiah 17:9). Therefore, if a person has a pure heart, God must have given it to him in regeneration. Jesus told Nicodemus plainly that the only people who can see or enter the kingdom of God must have been born again. 

Finally, it is against fallen human nature to seek peace. Our old nature is violent and enjoys violence. If a person seeks to make peace between fellow men, he is showing the new nature of Christ that dwells in him. This love of brethren is a clear evidence to all that someone is a disciple of Jesus. 

"By this shall all men know that ye are my disciples, if ye have love one to another." (John 13:35)