These are very strong verses which leave no room for compromise.  Jesus is clear that there is no middle way (somewhere between loving Jesus and hating Him).  It does not exist.  Those who do not work with Jesus are working against Him, having an anti-Jesus effect on others, and discouraging them from following Him.  Those who will not identify with Jesus are against Him; they are His enemies.  However, they can turn and repent; and if they do, they will be forgiven.
 
God’s forgiveness is available to everybody who admits that they are wrong, whatever the sin.  But there is one exception: blasphemy against the Holy Spirit.  What is that?  A number of suggestions have been made, but the context of the verses should help our understanding.  Luke places the words, “Whoever is not with me is against me, and whoever does not gather with me scatters” (Luke 11:23) in the middle of Jesus’ explanation that His ability to drive out demons was from God and not Satan – because Jesus had just been accused of being demonised (Matthew 12:22-28).  They had wrongly said He was able to perform miracles because Satan had given Him power.
 
That was the absolute opposite of the truth.  Jesus had come to defeat Satan, not serve Him or collaborate with him (Matthew 4:1-11).  By refusing to see who Jesus was, they blasphemed against the Holy Spirit, who is the Spirit of truth (John 16:12-15), by saying that He was evil.  Although they had seen the Son of God acting with divine authority, their false conclusion prevented them being included in the holy fellowship of the Spirit of God with the Son of God (John 17:20-23).  Without repenting of sin, accepting the conviction of the Holy Spirit, there is no possibility of forgiveness (Acts 13:38).
 
We must be clear about who Jesus is and our responsibility to repent of all false beliefs about Him.  Our eternal destiny depends on that understanding.  He cannot be reduced to being just a good teacher or an inspired prophet: He is God who lived within the constraints of a human body, so that He could die for our sins.  Refusal to accept His deity is to deny the essence of His nature; and without believing in Him and welcoming Him, nobody can be saved (Acts 4:12).