Rev21:18b;"And the City was Pure Gold,like clear glass"
The City is the New Jerusalem,Gold signifies that which is of God.
Peter said we are partakers of His Divine Nature(2Ptr1:4).within every born again Christain there is a portion which is of God.before we are saved,everything in us was of the Flesh,nothing of His Divinity is in us.but,when we recieved  Him as our Lord and saviour,He imparted His Life(or Nature) to us,which is the Gold in us.
Although we have Gold as Gold in us,its still mix with many other things in our body.for this reason majority of God's work in  our life is that of reduction and not addition.from the day we are saved God have been doing the work of reduction in our life and the instrument of this work of subtraction is the Cross.the work of the Cross is to cancel out all thats not of God in our life by the power of the Holy Spirit.
Paul said,"our old man(nature)has been Crucified with Him(Rom6:6).And we should reckon ourselves dead to sin,so that the remnant will be Christ our Lord.(Rom6:11).There are many things not of God in us which won't bring Glory to Him.what He deposited in us is Pure Gold,but because of the dross in us,we have become alloy.
The outstanding feature of the New Jerusalem is Pure Gold.there is no mixture everything is entirely of God.all that comes from  us is dross,apart from the Gold in us everything else is refuse.
When added to Gold our Goodness and zeal becomes dross.
Every thing from us is just  dross.but in the New Jerusalem all is of Pure Gold without any dross.
May His Spirit perfect His works in us through the principle of subtraction by the Cross inorder that the remnant will be Christ Jesus the only true Pure Gold in our life Jesus name Amen.