Romans 6:12-13 — Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof.
Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God.
Up until now, Romans 6 spoke of the heart; now the emphasis shifts to the will.
mortal = liable to death, but also with the sense that the body is the organ in and through which sin works.
lusts — any desires inconsistent with the will of God.
yield (1st usage) = present, voluntarily put at the disposal of. It's in the continuous tense — something you do day after day. Yielding is living objectively, accentuating the positive. This isn't a feeling, but an occupation with spiritual things. Do spiritual things to keep yourself out of mischief. Galatians 5:16 — This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
instruments = weapons
yield (2nd usage) — tense indicates a deliberate act (once for all) with lasting results.
God never asks anything of the unbeliever but absolute acknowledgment of his complete ruin in sin, and of God's perfect remedy in Christ. But when we have unconditionally surrendered to the doctrine of ruin and redemption, the Lord calls us away from the old patterns of life, establishes us in a new framework of righteousness, and enables us to live as befits our new position. — Donald Grey Barnhouse, God's Freedom, pg. 124