When we speak that there must be a necessary change when a person trusts in Christ there is often an undercurrent of distinction between the message of Jesus and the teaching of Paul. Advocates for looking toward Paul for the Gospel (and not the messages of Christ) will appeal to the sections of Scripture like Romans 3 and 4 because it is in these chapters we see the clearest picture of justification by faith alone. The reasoning goes something like this, “if there must be fruits of obedience to express a person truly being justified, then Paul would have most certainly included that teaching in these chapters.” At this point, a citation of a teacher(s) such as Dr. J. Gresham Machen (Presbyterian from the Reformed tradition, a scholar, and defender of the faith; 1881 to 1937) will be quoted to support this belief:

“Nothing before the cross can properly be called the gospel.”

So, is Jesus trumped by Paul when it comes to truly expressing the Gospel message?

I rest assured that whatever Dr. Machen meant by this comment, he did not believe that the Gospel that Jesus gave was preparatory and, therefore, somehow deficient to “Paul’s Gospel”

I know that some people hold—by a veritable delirium of folly, as it seems to me—that the words of Jesus belong to a dispensation of law that was brought to a close by his death and resurrection and that therefore the teaching of the Sermon on the Mount, for example, is not intended for the dispensation of grace in which we are now living.
Well, let them turn to the apostle Paul, the Apostle who has told us that we are not under the law but under grace. What does he say about the matter? Does he represent the law of God as a thing without validity in this dispensation of divine grace? Not at all. In the second chapter of Romans, as well as (by implication) everywhere else in his Epistles, he insists upon the universality of the law of God. Even the Gentiles, though they do not know that clear manifestation of God’s law which was found in the Old Testament, have God’s law written upon their hearts and are without excuse when they disobey. Christians, in particular, Paul insists, are far indeed from being emancipated from the duty of obedience to God’s commands. The Apostle regards any such notion as the deadliest of errors. “Now the works of the flesh,” says Paul, “are manifest, which are these: Adultery, fornication, uncleanness, lasciviousness, idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.”
J. Gresham Machen, The Christian View of Man (Edinburgh: Banner of Truth, 1937), 186–87. Cited by MacArthur, J., F. (1997, c1988). The Gospel according to Jesus. Zondervan Pub. House.

Consider what Augustine, writing in A.D. 412, described as the works of righteousness as an inevitable proof of the operation of the Holy Spirit in one’s life:

We for our part assert that the human will is so divinely aided towards the doing of righteousness that, … besides the teaching which instructs him how he ought to live, he receives also the Holy Spirit, through which there arises in his heart a delight in and a love of that supreme and unchangeable Good which is God; and this arises now, while he walks by faith and not by sight. That by this earnest, as it were, of the free gift he may burn to cleave to his Maker, and be on fire to approach to a share in that true light.… But to the end that we may feel this affection “the love of God is shed abroad in our hearts” not “through the free choice which springs from ourselves,” but “through the Holy Spirit which has been given to us” (Romans 4:5).

So, those who will create two Gospel presentations as a way to dumb-down the radical nature of Christ’s call, and subsequent evidence supporting a true change in the life of the adherent, have no leg to stand on when it comes to the historical record. Anyone who wants to create a “stage 1” and “stage 2” approach to the Gospel are simply wrong. We must be ready to gently help people who have been under this type of teaching to not minimize Jesus’ teaching. I believe when we pit Jesus and Paul against each other in this way we actually play into the hands of the enemy.

BTW.
We see this same dynamic in place by other groups of people who advocate the need to minimize the sinfulness of homosexuality in the life and expression of the Church. How? By stating that Jesus never spoke expressly against homosexuality and, therefore, He was accommodating to it. Those who hold this position will acknowledge that Paul certainly did speak against homosexuality, but since Jesus didn’t it must be a secondary issue. Hence, Jesus trumps Paul.