“Grace wherein we stand” (Rom 5:2; 1 Pet 5:12) is not attempting to completely disassociate our words and actions from sin, as if this were expected or even possible (1 john 1:8); nor is it to empowers us to overcome sin (not the same as “overcome evil”, the product of sin), something which only the Lord could do and has effected for us. Grace is to realize our forgiveness from its guilt and our deliverance from its rule and I believe to expect anything beyond this is to be “unskillful in the word of righteousness,” because it is unscriptural.
Romans-Eight is a comparison between those who are not in Christ and those who are. Verse 13 is not an admonishment to the believer to avoid walking “in the flesh,” it is a description of one who is not in Christ because those who, “are in Christ Jesus” are those, “who walk not after the flesh, but after the Spirit” (v 1).
When we try to oppose sin with our own strength and will, we abrogate the supply of atonement which has already sufficed the Father and thus, are attempting to walk in our own provision and will lack “having always a conscience void of offence toward God and toward men” (Acts 24:15). Appropriating Christ’s deliverance in place of attempting our own is not to advocate passivity to sin, but allows the Spirit to “mortify” it, rendering its control powerless. The manifestation that the Spirit is “mortifying the deeds (actions) of the body” in a believer will be evident in his words and deeds (Matt 12:33; Luke 6:44) —the greatest deed being that in John 15:12, “This is my commandment, that ye love one another, as I have loved you.”
J Gill-- “For if ye live after the flesh, ye shall die” ... “Such persons are dead, whilst they live and shall die a second or an eternal death, if grace prevent not. It may be asked whether one that has received the grace of God in truth, can live after the flesh. Flesh, or corrupt nature, though still in such a person, has not the dominion over him, to live in sin, or in a continued course of sinning, which is contrary to the grace of God. But flesh may prevail and greatly influence the life and conversation, for a while, how long this may be the case of a true believer, under backslidings, through the power of corruptions and temptations, cannot be known, but certain it is that it shall not be always thus with him. It may be further inquired, whether such a one may be so left to live after the flesh, as to die and perish eternally. Christ expressly says, such shall not die that live and believe in him, for grace, which is implanted in their souls, is an incorruptible and never dying seed and grace and glory are inseparably connected together.”