1 John 4:20

If anyone declares, 'I love God,' and yet hates his brother, he is a liar; for he who will not love his brother whom he has seen, cannot possibly love the God whom he has never seen.

1 John 2:4

He who says, 'I know him,' but does not obey his commands, is a liar and the truth is not in him;

1 John 2:9

He who says he is 'in the light' and hates his brother, is in darkness still.

1 John 3:17

But whoever possesses this world's goods, and notices his brother in need, and shuts his heart against him, how can love to God remain in him?

1 John 4:12

God no one has ever seen; but if we love one another, then God remains within us, and love for him is complete in us.

1 John 2:11

but he who hates his brother is in darkness, he walks in darkness and does not know where he is going, for the darkness has blinded his eyes.

1 Peter 1:8

You never knew him, but you love him; for the moment you do not see him, but you believe in him, and you will thrill with an unspeakable and glorious joy

1 John 1:6

If we say, 'We have fellowship with him,' when we live and move in darkness, then we are lying, we are not practising the truth;

Treasury of Scripture Knowledge

Summary

If a man say, I love God, and hateth his brother, he is a liar: for he that loveth not his brother whom he hath seen, how can he love God whom he hath not seen?

Bible References

A man

1 John 2:4
He who says, 'I know him,' but does not obey his commands, is a liar and the truth is not in him;
1 John 3:17
But whoever possesses this world's goods, and notices his brother in need, and shuts his heart against him, how can love to God remain in him?

Not

1 John 4:12
God no one has ever seen; but if we love one another, then God remains within us, and love for him is complete in us.

General references

Matthew 22:40
The whole Law and the prophets hang upon these two commands."
Matthew 25:42
For I was hungry but you never fed me, I was thirsty but you never gave me drink,
John 13:35
By this everyone will recognize that you are my disciples, if you have love one for another."
John 14:15
If you love me you will keep my commands,
Hebrews 13:1
Let your brotherly love continue.