8 Now if we died with Christ, we believe that we shall also live with Him,
“Now” advances the argument. We cannot separate forgiveness of sin from the spiritual life of walking daily with the Lord.
if [since] we died
We “died” with Christ at one point in the past (aorist indicative). It is already a fact that believers died when Christ died. This is just one of a series of point actions in the past by Christ on our behalf that we have seen in this chapter (vv. 2, 3, 4, 6). We died by virtue of the truth that Jesus died for us. However, our death with Christ is not an end in itself; we died with Christ for a purpose—ongoing life of fellowship with Christ.
The “with” in the phrase “with Christ” carries the idea of our having died in company with. We were in the company of Christ when He died.
Co 2:13, And you, being dead in your trespasses and the uncircumcision of your flesh, He has made alive together with Him, having forgiven you all trespasses . . .
Co 3:3-4, 3 For you died, and your life is hidden with Christ in God. 4 When Christ who is our life appears, then you also will appear with Him in glory.
we believe [keep on believing] that we shall also live with Him,
Paul changed the emphasis here from dying with Christ to living with Him. Since it is an accomplished fact that we hold the status of having died with Christ, then it follows that we will “live together with Him.” The word “also” implies that, in addition to living the resurrection life in time, we will live with Jesus in eternity. Resurrection life begins at salvation and will continue into eternity. We participate in His resurrection life in time and eternity.
Living with Christ in eternity should start with living with Him now.
Our life with Christ now will be more wonderful when we spend eternity with Him. However, why not start to enjoy life with Christ now? It is a necessary outcome of a person becoming a Christian that he fellowship with the Lord. There is no justification that, since God gives super-grace (Ro 5:20), we abuse that grace because of what our wonderful Lord accomplished for us.