Good morning Hammster. I hope you had a blessed evening.
Just looking at the verse you presented as data for your assertion. It appears to me that the verse in and of itself may be lacking as the only verse needed. But maybe it doesn't. I'll think through it as I write.
It would appear that Paul, in his letter to the Romans, is speaking to Christians. That is, those that already believe and have the Spirit within. He writes in Romans 8:1-2,
"For the law of the Spirit of life has set you free in Christ Jesus...". So these readers he is addresssing already have the Spirit of Christ unto eternal life (or he assumes such).
In Romans 8:3-4 it appears that Paul speaks about the salvation part unto the Christian walk, speaking to how the Spirit has done what the law could not, but then goes on in v4 to say that the Spirit has accomplished this so the
"righteous requirement of the law might be fulfilled in us". And the righteous requirement of the law is fulfilled so that those are able to not
"walk not according to the flesh but according to the Spirit" (Rom 8:4).
Then in Romans 8:12-13 Paul writes,
So here is the point I'm trying to get too. Christians already have the Spirit. The Spirit is within them doing the Spirit's work. But Paul is telling these Christians to not live according to the flesh.
(1) Christians already have the Spirit
(2) Christians can either live according to the Spirit or according to the flesh. For Paul bascially tells them to not live acccording to the flesh.
This concept of rebucking Christians who have received the Spirit but don't walk in the flesh is common within Paul's writings. In Paul’s vernacular this is expressed as,
“therefore…we also should walk in newness of life” (Rom 6:4), and also present oneself
“to God as being alive from the dead” (Rom 6:13), and one should also present one’s
“members as slaves of righteousness for holiness” (Rom 6:19) which is one’s
“reasonable service” (Rom 12:1).
So with the Spirit at work, faith is needed for God to be pleased. Or as James puts it,
"faith was active" (Jam 2:22). So if it is the case that the Christian has the Spirit within yet needs and active faith for God to be pleased, then it would follow that for God to be pleased the spirit and the act of faith is required.
But you want to apply what God says about a Christian walk, walking in the flesh or walking in the Spirit and apply it to the unbeliever (that becomes a believer). But are they both enough the same to do such? At least with this verse only?
My apologies, I must end this post. Have other life issues that need attention. I'll be back later.
May God do a fruitful work through you, my brother.