Love is the major and ineradicable constraint on the Christian possibilities of this mortal life.
By which I mean that it is the intrinsic limitations of our ability to love in this-life; that mean "Heaven on Earth" is not just difficult but impossible
It is the limits of our ability to love that - to various degrees - constrain our ability to live a Christian life.
Our love - here on earth - is always and necessarily, due to the presence of evil and entropy - Personal and Partial.
Our capability for love is incomplete, and often very incomplete; and the strength and endurance of our love is sometimes (or often) weak - so that the pressures and evils of this-world are capable of overcoming the strength of our love (sooner or later).
And the partial nature of our love greatly limits the possibilities of goodness. For instance, love is needed for proper motivation; and our will-power and choices will be wrong if they are not motivated by love.
Furthermore, some individuals are more loving than others, and some have more powerful love than others; so that some individual people are capable of only rather weak love of only a few persons or other Beings - perhaps loving just one single person, or animal. This does not prevent such a person from following Jesus to Heaven.
(Only one who was incapable of love, or one who refused to love, would be unable - as well as unwilling - to attain salvation.)
Furthermore love just-is, by its nature, personal - in the sense that real love is between particular Beings. This can be illustrated by the Fourth Gospel where, in every instance that it is mentioned, Jesus's love is personal and particular.
This means that (in this mortal life on earth) our loving motivations are always particular; and (given the nature of our lives) this means that we are required to do many/most things for which we are not motivated by love at all.
(And without love, there will not be Good. For instance, prayer or meditation not motivated by love, will do not Good - and may do harm.)
Indeed, we are all ineradicably prone to all kinds of un-loving attitudes against other people, animals, plants and "minerals"; from regarding them as un-alive and un-conscious, to desiring to manipulate and exploit them for selfish - or other - ends; to desiring to inflict harm from resentment and spite.
Thus, real love is personal and during the earthly life it is partial; so that we cannot as mortals "live by love".
Furthermore; this problem is not solved by reducing the actuality of real love to abstractions; e.g. by declaring that the "higher" love (the best, or really-real love) is Universal and Unconditional.
People try to evade the constraints of actual love in this mortal life, by declaring that love ought to be, and can be, Universal - so that we love everybody and every-thing; and that it should be Unconditional - coming from-us, all the time, in all situations, regardless of persons or motivations.
UU-Love is just something else than real love - it is neither Christian, nor Good. UU-Love is, indeed, associated with Oneness spirituality - which is not Christian but derives either from pagan sources (such as Pythagoras and Plato) and/or from "Eastern" religions such as Hinduism and Buddhism.
That which is universal and unconditional is not love, at least not for Christians; because real love is personal, between Beings; and not, therefore, the kind of thing that can be had by decision, declaration, or on-principle.
Heaven is a place or state in which love motivates all thought and deeds. That love is indomitable, permanent, and it remains personal in nature. But in Heaven, we love all the persons (all the Beings) in Heaven.
That's what makes it Heaven - at resurrection, every Being has left-behind all that is not of-love
(Loving not-equally, of course - e.g. the wholly-loving mortal Jesus loved some men and women more than others.)
As Christians we need not be ashamed-of, nor try to conceal, that our love in this mortal life on earth is PP-Love.
Nor should we be tempted by that fake love which masquerades as Universal and Unconditional.
After all; if a state of complete love of all were possible on earth; then the salvation offered by Jesus would not have required that we first die, then be resurrected to Heaven!
