We Christians do have a code of conduct which we are to live by. But it is a code of conduct which we can only gain the ability to follow as a direct result of our accepting the gift of salvation exactly as God offers it:
Now we know that whatever the law says, it says to those who are under the law, so that every mouth may be silenced and the whole world held accountable to God. Therefore no one will be declared righteous in his sight by observing the law; rather, through the law we become conscious of sin.
But now a righteousness from God, apart from law, has been made known, to which the Law and the Prophets testify. This righteousness from God comes through faith in Jesus Christ to all who believe. There is no difference, for all have sinned and fall short of the glory of God, and are justified freely by his grace through the redemption that came by Christ Jesus. God presented him as a sacrifice of atonement, through faith in his blood. He did this to demonstrate his justice, because in his forbearance he had left the sins committed beforehand unpunished - he did it to demonstrate his justice at the present time, so as to be just and the one who justifies those who have faith in Jesus. (Romans 3:19-26,NIV)
It is only through our accepting the atoning sacrifice of Jesus Christ as the means of cleansing us of our sins that we have assurance of salvation. This cannot be augmented, nor can it be replaced by anything else we might do. God accepts only the blood of his Son, Jesus Christ, as the perfect atonement for our sinfulness. Everything else must begin here.
Upon our accepting the gift of salvation as God offers it, God sends his Spirit to dwell within us, and it is this bonding of his Spirit with us that enables us to conduct ourselves in accordance with his will. And that is due not to our becoming legalistic; that not only didn't work before, but also was abused by those whose desire was to have absolute power over others. Instead, we are given the spiritual equivalent of a heart transplant, with our old nature being subdued by the Spirit while a new nature is implanted within us. And it is only with this new nature that we can conduct ourselves as God wants of us:
So I say, live by the Spirit, and you will not gratify the desires of the sinful nature. For the sinful nature desires what is contrary to the Spirit, and the Spirit what is contrary to the sinful nature. They are in conflict with each other, so that you do not do what you want. But if you are led by the Spirit, you are not under law.
The acts of the sinful nature are obvious: sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God.
But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control. Against such things there is no law. Those who belong to Christ Jesus have crucified the sinful nature with its passions and desires. Since we live by the Spirit, let us keep in step with the Spirit. Let us not become conceited, provoking and envying each other. (Galatians 5:16-26,NIV)
The motivations listed as 'the acts of the sinful nature' are the underlying origin of all sinful acts. No action which has any of these motivations as its impetus can be seen as anything other than sinful, just as a poisoned tree cannot yield good fruit. But they are also the motivations which are at the core of our original, sinful nature, and as such are as much a part of us as our eye color. So we need for the Spirit himself to 'rein them in' rather than accomplishing this task ourselves. And this the Spirit does willingly as a result of our accepting Jesus' sacrifice as the atonement for our sins.
But not only does the Spirit 'rein in' our sinful nature, but he also implants within us a new nature. This new nature is 'the fruit of the Spirit', and has its own set of motivations. It is when these motivations are the impetus for what we do, and only then, that our actions have assurance of aligning with God's will. It's not enough for us to do the right things; we must also do them for the right reasons. And it is when the motivations listed as 'the fruit of the Spirit' are the origin of our actions that those actions have the right reasons as their impetus. The supreme importance of the 9 'fruit' to us is emphasized by the words which immediately follow their listing: "Against such things there is no law."