John 6:37; Ephesians 1:13; Romans 8:29-30, 35-39; John 6:66; 1 John 2:19
A piece of coal cannot, by its own will (decision or declaration), turn itself into a diamond; and a diamond cannot turn itself back into a piece of coal. If a piece of coal is turned into a diamond, that diamond cannot be turned back into a piece of coal—let alone by its own efforts and merits. The question that needs to be asked is, was that piece of coal turned into a diamond? Just because a piece of coal says, "I'm a diamond," does not make it so! Just because it covers itself in a shiny coating (behavioural modification) does not make it a diamond. God is the potter, we are the clay. If He turns a piece of coal into a diamond, it is a diamond for all eternity.
Here are the facts for those who need to read their Bibles more carefully, and to do so in context. It is God Who saves. Without God working in you first, you would not be able to respond to the Gospel (John 6:44, 65). You can only respond once God has changed your heart. When God regenerates you, makes you born again from above, gives you a heart of flesh, and makes you spiritually alive, there is nothing that you can to to alter any of that! You are not God! You are not more powerful than God! Anyone who suggests otherwise is putting man above God, saying that man can thwart the will of God. Man's will cannot contend with God's will. That would be like a dandelion contending with a lawnmower. The person who suggests otherwise does not know God or man, let alone their Bible.
People who think you can "lose" or forfeit your salvation do so because of a failure to understand the teachings of Scripture. They fail to understand apostasy and do not seem to grasp the concept of false converts. Take Hebrews 6:4-6 for example: Instead of asking, "Can an unbeliever be enlightened, taste the heavenly gift, partake of the Holy Spirit and taste the powers of the age to come?," try asking, "Can the unsaved, or false convert, be enlightened, taste the heavenly gift, partake of the Holy Spirit and taste the powers of the age to come?" The answer is, "Yes!" One of the soils is described in precisely this manner.
Also, people who suggest that man's will can contend with God's will and thwart it, using parables as their proof text, need to study hermeneutics and exegesis. Your theology cannot be derived from parables. That is a foolish approach to Scripture. This is a common error from those who have no gifting as a teacher and think that anyone reading the Bible can interpret it correctly. If that were true, there would be no need for teachers. Those confused about John 15 should read this.
If it were possible to "lose" or forfeit your salvation, John 6:37 would be false. “ALL that the Father GIVES to Me WILL COME to Me.” The giving precedes the coming. “All” means that there will not be one more or one less, which would be the case if we, by our own merit, could lose salvation. If you think “God’s a gentleman” Who only invites but never forces, I suggest you look at Paul’s life where God kicked in the door to his heart, where Paul later writes that God had set him aside since birth for his mission.
See John 6:44, 65.