The key to understanding Leviticus 19:18, its quotation by the Lord as part of the great commandment, and the explanatory parable of the good Samaritan is often missed.
Matthew 22:37-39 (KJV) Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. And the second is like unto it, Thou shalt love thy neighbour as thyself.
How is the second like unto the first?
Our love for God is a passive love. We love Him for what we receive from Him. Including faith in His Son and the good works that He has prepared for us to walk in.
But most would have the love of neighbor and self be the opposite kind of love, a love that gives, an active love, doing things for others as we do things for ourselves.
If the second is like unto the first, it is a passive love, a love of receiving.
We love our neighbors and ourselves because these are channels of God's gifts and His love to us.
We love everything about ourselves because this is the way that God made us.
We love everything about all our neighbors because they are also God's gifts to us, beginning with our parents.
We have faith that the defects in ourselves and in our neighbors are part of God's purpose in which all things work together for good to them that love God and are the called according to his purpose.
There is a seemingly odd phasing in the parable of the good Samaritan that supports this.
Luke 10:36 (KJV) Which now of these three, thinkest thou, was neighbour unto him that fell among the thieves?
The question is not what the common interpretation of love of neighbor would dictate: "Which regarded the man who fell among thieves as his neighbor (and actively loved him)?"
But the lawyer, like just about everybody, all focused on works religion and guilty of the error of the Galatians answered the substitute question of his imagination.
(And the Lord passed over this error as He did a similar error by the rich young ruler who also believed in works and ignored a similar hint that the Lord gave, " Why callest thou me good? none is good, save one, that is, God." (Luke 18:19) When we think that works are the way to go, often only long sad experience will convince us otherwise. Our Lord realized this and did what He could for these people, leaving an important message for those who will examine these passages prayerfully and carefully.)
Actually the man who fell among thieves should love all three. The priest represented him in the Temple before God. The Levite took on the temple duties that would otherwise be done by his firstborn son. Each in his own way and despite defects (the Samaritan worshiped in the wrong place) was a channel of God's love. Each was a neighbor, placed there by God.
