Gibbs, Jeffrey A. “Matthew 5:43-48: On Love." Matthew 1:1-11:1. St. Louis: Concordia Publishing House, 2006, pp. 304-308.
Commenting on Matthew 5:43, Gibbs points out that Jesus is specifically not quoting the Old Testament. The only use of the verb form here in the Old TEstament is Leviticus 19:17, which says not to hate your brother (Gibbs 2006, 304). Gibbs concludes that Jesus is citing some teaching found in 1st century Judaism. Jesus' contrasting command, to love your enemies, is clearly something which goes against virtually all of our sensibilities (Gibbs 2006, 305). Gibbs also observes the purpose of this love, that it shows the relationship to the loving Father in heaven. It further shows a sign of Jesus, who loves his enemies and gives himself for them.
The reality of hatred is clear in the Scripture. Gibbs notes that it is rightly directed toward evil, though we are never commanded to hate our enemies (Gibbs 2006, 306). There are, of course, many statements affirming that the wicked hate God and His people. Counter to this, Jesus commands his disciples to love and pray for others. Verse 48 "follows from Jesus' earlier commands to love the enemy, since the Father willingly does good to all" (Gibbs 2006, 307). In this, it shows love for others as the sign of maturity, being like God.