Can't I be rich? Is that a Sin?

Beloved, in regard to all things I pray that you prosper and be in health, even as your soul prospers.
(3 John 1:2 MKJV)

Having success isn't a sin. King David was successful and God said to him through the prophet Nathan, "I anointed you king over Israel, and I delivered you out of the hand of Saul. And I gave you your master's house and your master's wives into your bosom, and gave you the house of Israel and of Judah. And if that was too little, I would have given to you such and such things besides." (2 Sam. 12:7-8)

God also blessed Job with double after He took him through hell on Earth, "And Jehovah blessed the latter days of Job more than the beginning." (Job 42:12)

Will God prosper and bless those under the old covenant and not those under the newer and better coventant?

"...He (Jesus) is also the Mediator of a better covenant, which was built upon better promises." (Heb. 8:6)

and,

"For all the promises of God in Him are yes, and in Him Amen, to the glory of God by us." (2 Cor. 1:20)

then finally we have this very awesome promise concerning Jesus and the believer,

"Truly He who did not spare His own Son, but delivered Him up for us all, how shall He not with Him also freely give us all things?" (Rom. 8:32)

So, we see through these verses and very simple reasoning that God will bless the believer in this age. There are still many more verses, that can be added like the passage in the gospels where Jesus said that we will receive many things in this life plus much more in the one to come. (Mat. 19:29; Mark 10:30; Luke 18:30)

But how then do we reconcile this with what Jesus also said in Luke 18:22, "And when Jesus heard these things, He said to him, Yet you lack one thing. Sell all that you have and distribute to the poor, and you shall have treasure in Heaven. And come, follow Me."

What we need to understand is that Jesus never taught His disciples to live a life of poverity. He always taught to expect great blessings from the Father. What He did teach was that these Earthly treasures are temporal and subject to corruption and theft. He also taught that men's hearts can cause him/her to be carried away by it's worries over the stability of this world's financial systems(Mark 4:3-20; Jam. 1:11).

Jesus promised us that He has an inheritance stored up for us in Heaven. There are also rewards for faithful service while we are bound here on Earth. However, I fear, many of us are thinking that these rewards are easy pickin's, not so. From what I read in the scriptures, these rewards will be given mostly to those who have labored to seek the difficult path that few will find (Heb. 11:24-26; Matt. 7:13-14; Luke 14:27; Mark. 3:32-35;).

What I see in Scripture is that Jesus has warned us that the things of this world are seductive and deceptive. There is good here, but He is preparing a New Heaven and New Earth that will be our inheritance and home. This is the "true riches" that we should be looking forward to. He teaches that when we don't have faith to trust in this that it disappoints Him and He sees it as a lack of faith on our part(Matt. 10:32-33; Luke 12:8-9; Mark 8:38, 16:14).

-Selah