Galatians 4:7

"So you are no longer a slave but a child, and if a child then also an heir, through God."

Under Roman law, an adopted child was treated like any other member of the family and guaranteed all legal rights to his father's property, even if he was formerly a slave. We in our human nature often are slaves to sin as we let sin govern our lives (Ref 2 Pet 2:19).
 
Jesus taught us to pray "The Our Father" (Mt 6:9-15); 'Abba' is an Aramaic word for 'Father' and so He made a way for us to become the children of God. He completed this act, by dying on the cross and rising again in three days; defeating sin, death and satan once and for all thus ransoming us from the slavery of sin and making us the true children of God. As adopted Children of God we share with Jesus all rights to God's Kingdom. As God's heirs we can claim what he has provided for us - our full identity as His children (Rom 8:15-17). 
All we need to do is accept Jesus and beleive in him as our only Saviour in order to be identified as God's children and thus His heirs.

Congratulations on accepting Jesus as your Lord and Saviour. You are now an "Heir to the Kingdom of God.”