Why is the law fulfilled in believers if they aren't better at keeping it than Israel was?

Les explains that the law is fulfilled in us not because we are better at law keeping than Israel was, but because of our position and because of the power of the Holy Spirit. We no longer walk after the flesh or after old Adam, but after the Spirit. Old Adam was crucified and in God's eyes is completely dead and out of the picture, though in our experience he is still here; he is defeated and does not have to remain uppermost. If he remains uppermost, it is because we are not fighting the battle. The Holy Spirit came in and empowered our spirit, and the Holy Spirit working in consort with our spirit enables us to live victoriously. Old Adam is powerful and will come to the fore at times, and that is where the warfare exists. Without the indwelling Holy Spirit, there would be no warfare or battle line, and we would not stand a chance against the forces of old Adam and Satan. Les also notes that in the Greek it is the Pneuma Hagion, meaning power from on high.