When one's belief conflicts with an "Authority" one's belief is not necessarily wrong.. so you have made a logical error.
How does this relate to the differing perspectives held by Jesus and Paul w/r to salvation ?
One thing I might say in Paul's Defense though is that I am not convinced that even Paul would accept the doctrine "Sola Fide"
You are right to say the "authority" is not the definer of truth. But in spiritual things there are perspectives that are difficult to grasp.
The example is in the phrase "you know everything".
We all know it is impossible to be able to define and know everything. So that meaning, unless spoken in a sarcastic manner means you know things that others do not, and are the definer of meaningful knowledge. A lot of our language and idioms are defined in these cultural ways and discussions around what is possible and what is not, what a community knows and is focused on, and what is irrelevant and what is to the point.
Scripture by the nature of how God expresses himself is full of these focused points of emphasis and meaning. So the Father is "I am", the ever present and existent one, the ultimate reference point for everything. The Lord lays down levels of respect and authority, starting with Himself. His emphasis is on approach, not knowledge or content, but approach. Emotionally so many of our failures come from getting these issues wrong.
A for instance is sexual attraction. Two people connect, and are strongly attracted to each other. As they discover who each is, they realise this is a physical reaction and as people they are the opposite of who they would be with or want to be with, and have zero future together. Now how do we avoid such split perspectives? Or family loyalty over morality and truth. Jesus said we should hate such loyalty when in conflict with things of God. So on every scale love of God and His ways stands preeminent above everything else.
These are emotional perspectives and how we live them out, rather than "facts" or "truth". Now to see God, to know His will, Jesus put as the foundational stone purity, being clean, standing apart, seeing things as a whole, being objective and knowing the beginning and its consequences.
Once you begin to see this is the foundation, a lot of what one sees as contradictions become nuances on the interaction between different approaches and situations. One begins to see that murder is defined on the individual scale of rights of an individual over another, but as a community fighting for existence to the death is acceptable. So justice and love are two different perspectives of the same reality, but often lead to different behaviours and reactions, depending upon the role one is playing.
It is easy in the moment to see a rebellious teenager asserting their independence and someone who needs to be loved and given space. Finding a way through, being able to know how things will develop and limiting damage and words, to a time when the reality of bonds and investment can be better reflected. I have lived these very realities, and after seeing the person behind the words, changed how I responded, and the push back I gave.
So I have seen Jesus and Paul as different people preaching a contradictory emphasis and now see a coherent whole, with different ministries at different times in the life of the Kingdom. God bless you
and what a nonsense term... Excuse for what. You are the one trying to excuse blatant contradictions - interpolation, "sin of omission" and outright pious Fraud ... via conflating my suggestion of going with what one likes on a personal level - as some kind of refutation to the above Fact. 
