Matthew 22:34-40 (ESV)
34 But when the Pharisees heard that he had silenced the Sadducees, they gathered together.
35 And one of them, a lawyer, asked him a question to test him.
36 “Teacher, which is the great commandment in the Law?”
37 And he said to him, “You shall love the Lord your God with all your heart and with all your soul and with all your mind.
38 This is the great and first commandment.
39 And a second is like it: You shall love your neighbor as yourself.
40 On these two commandments depend all the Law and the Prophets.”

1 Corinthians 13:1-3 (ESV)
1 If I speak in the tongues of men and of angels, but have not love, I am a noisy gong or a clanging cymbal.
2 And if I have prophetic powers, and understand all mysteries and all knowledge, and if I have all faith, so as to remove mountains, but have not love, I am nothing.
3 If I give away all I have, and if I deliver up my body to be burned, but have not love, I gain nothing.

Who do we love?
1. Brothers:
1 John 4:7-8, 20-21 (ESV)
7 Beloved, let us love one another, for love is from God, and whoever loves has been born of God and knows God.
8 Anyone who does not love does not know God, because God is love.
20 If anyone says, “I love God,” and hates his brother, he is a liar; for he who does not love his brother whom he has seen cannot love God whom he has not seen.
21 And this commandment we have from him: whoever loves God must also love his brother.

2. Neighbors:
Luke 10:36-37 (ESV)
36 Which of these three, do you think, proved to be a neighbor to the man who fell among the robbers?”
37 He said, “The one who showed him mercy.” And Jesus said to him, “You go, and do likewise.”

3. Enemies:
Matthew 5:43-48 (ESV)
43 “You have heard that it was said, ‘You shall love your neighbor and hate your enemy.’
44 But I say to you, Love your enemies and pray for those who persecute you,
45 so that you may be sons of your Father who is in heaven. For he makes his sun rise on the evil and on the good, and sends rain on the just and on the unjust.
46 For if you love those who love you, what reward do you have? Do not even the tax collectors do the same?
47 And if you greet only your brothers, what more are you doing than others? Do not even the Gentiles do the same?
48 You therefore must be perfect, as your heavenly Father is perfect.