There is a tendency to regard the injunction that Christians should Love One Another as something like a Law, imposed upon Man - with the main significance being that if you break the Law, then you will be 'sent' to Hell*.
Certainly that seems to be the way that this is used against Christians: non-Christians and anti-Christians are forever accusing Christians of insufficient love towards all-other-people.
Yet the appearance of the phrase Love One Another within the Fourth Gospel shows that that meaning can't be the one intended as primary.
Here is the context:
John 13:31 Therefore, when he was gone out, Jesus said, Now is the Son of man glorified, and God is glorified in him. 32 If God be glorified in him, God shall also glorify him in himself, and shall straightway glorify him. 33 Little children, yet a little while I am with you. Ye shall seek me: and as I said unto the Jews, Whither I go, ye cannot come; so now I say to you. 34 A new commandment I give unto you, That ye love one another; as I have loved you, that ye also love one another. 35 By this shall all men know that ye are my disciples, if ye have love one to another. 36 Simon Peter said unto him, Lord, whither goest thou? Jesus answered him, Whither I go, thou canst not follow me now; but thou shalt follow me afterwards.
Jesus is talking with his disciples about his own glorification - his ascension to Heaven. The new commandment to love one another is about what they need to do to follow Jesus to Heaven.
Love between Men seems to be a part of the 'process' by which Men can follow Jesus through death to life everlasting; presumably mutual love between the disciples it is a part of life everlasting.
To my mind, from its context; 'love one another' seems to be primarily (not exclusively) about life beyond death. The way I see it is that it is love for Jesus that enables Men to follow him through death; and love of 'one another' that makes this more than a solitary glorification. It is about the loving family of glorified men, following Jesus together.
It is not an injunction for everybody to love everybody, but a specific injunction for the disciples to love each other. We assume that 'love one another' applies to all followers of Jesus: that is to all disciples - but there seems nothing to suggest it goes beyond that circle.
And its importance is rooted in the life to come: which means that 'love one another is not about 'getting to Heaven' so much as what happens when we get there. Following Jesus is not a matter of escaping something we fear as it is a matter of joining something we want.
Love one another is therefore not really a passport to heaven (even less a get-out-of-Hell card); but a fundamental insight into the nature of life everlasting, which is being offered by Jesus. Because love is the basis and matrix of the New Life - it is what hold-together God's creation.
Love is analogous to the 'unified field' that supposedly makes the universe cohere and develop; but love is about relationships between persons: that is the ultimate metaphysical reality.
*Note: The Fourth Gospel doesn't use the word Hell, nor say much about the horrors of the life after death without Christ; nor a place of torment - even to his accusers whom Jesus characterises as children of Satan; but focuses almost-wholly on the 'benefits' of Life Everlasting, or 'Heaven'. The overall message is of a New Possibility, a possibility that must be chosen.