The promises and teachings of Jesus in the Fourth Gospel refer to the resurrected life eternal in Heaven - and not to this mortal life. How, then, does Christianity affect this, our mortal lives?
The answer is surely: indirectly, and as a consequence of our love of Jesus and our intention to follow him through death to everlasting life.
This means that the effect of Christianity upon this life flow from our Faith (belief-in, trust-in Jesus), from our Hope (that is, knowledge-of Heaven) and from Charity (love of Jesus, and the affirmed centrality of love of others in our lives).
In this sense, the implications for mortal life flow 'backwards' from the reality of post-mortal life. Because each person's life, situation and specific circumstances make for uniqueness; this means that we cannot say as an exact generalisation how this mortal life should-be affected by Christian faith.
We cannot derive a mapping of rules and principles from our Heavenly immortality onto our mortal evanescence.
Which is simply to say that Christianity is essentially of-the-heart; and not a matter of observable behaviours.
Now - this reality has often been taken a license of a claimed-Christian (or self-identified Christian church) to do anything they happen to want to do (typically something sexual or political), and to claim that 'it' is compatible-with, or dictated-by, ultimates. Such self-deception is so common as to be routine and mainstream; and forms the usual basis of apostasy of individuals and of churches.
But the individual is accountable before God, and his real-self which has agency - and at that level just consequences are unavoidable. So self-serving dishonesty is only a significant problem at the institutional level: and specifically in a set of Christian assumptions when the church is regarded as primary and definitive, the individual as secondary and obedient to church authority. And that is contradicted by the Fourth Gospel-centred understanding of Christianity.
When there is no church, or when the church is secondary to individual faith; there is no this-worldly advantage in falsely claiming that one's faith justifies some specific behaviour (or misbehaviour, as is more likely). After all, no external rules can prevent self-deception - as is clear from daily life.
The problem is worst when 1. a church claims authority; 2. that church claims that it is necessarily incorruptible in its essence and 3. when, in fact, that church is corrupt - in its essence (to a significant degree).
For example if a church is based upon a priesthood and that priesthood was replaced by atheist secret police, and the church remade as an instrument of state surveillance, propaganda and control (this was apparently, at times, the situation in the Russian Orthodox Church of the USSR)... Then it might be agreed that an attitude that 'Christianity' consists primarily of obedience to 'church'/ institutional authority - when such obedience is seen in terms of adherence to institutional practices, laws and rules - would probably lead to apostasy and damnation, rather than to salvation.
But if Christianity is regarded as primarily between 'myself' and God, and specifically in terms of my faith in Jesus Christ; then my mortal life will need to be judged in light of its post-mortal implications; and these just-are matters of the heart's discernment, and our actual life-situations just-are very specific rather than primarily category-based.
Christianity is, in this sense', 'not of this world' in terms of where faith is properly rooted. But there is all the difference in this world between Life conceptualised as restricted to mortality, and life which is leading to immortal resurrection in Heaven.
The difference is between (on the one hand) the totality of life as a matter of the inevitability of decay, disease and bounded by death and annihilation; and (on the other hand) an understanding of this mortal life as a preparation for an eternity spent as an immortal and divine Being, living with other divine Beings, and in creative participation with God.
The one reduces to hedonic and emotional here-and-now subjective psychology; the other expands to an expectation of objective divinity, responsibility, freedom and love.
This is important in explaining Christianity. Too often (and understandably) we fall into one of two errors: either explaining Christianity in terms of this-worldly behaviours and consequences leading to next-world consequences; or else of making Christianity something that is cut-off-from this world, with this-world behaviours 'merely' a matter of subjective-relativism, or temporary-importance hence indifference.
I find the best 'bridge' is in terms of the need for learning from this our mortal life; and that learning having objective and eternal consequences in the life to come.
Pute in one sentence: to aim to live in-light-of our expectation of resurrected eternal life, is to be a Good Christian.