Previously I failed to clearly distinguish between physical life and spiritual life, so I re-worded it below. I did not use the translation that speaks about
“never be lost” but I indirectly address it below:
Do the following verses show that we cannot lose salvation ?
“My sheep hear my voice, and I know them, and they follow me; and I give them eternal life, and they shall never perish, and no one shall snatch them out of my hand.”
The phrases “eternal life” and “they shall never perish” describe the gifts given to those who “hear” and “follow” Jesus, the One and only Savior. Only as long as one hears and follows Jesus do we have those gifts. Jesus has eternal life by the very essence of who He is, Life itself. The Christian possesses these gifts of eternal life and of never perishing in a way that is dependent on Jesus and dependent on remaining in a saving relationship with Him. If a Christian later rejects Jesus he then loses those gifts.
The early Christians lived in a time when life was hard. Without electricity to keep one’s food from spoiling or without the abundance of clean running water every individual had to be constantly aware of one’s own physical mortality. In 2 Corinthians 11:23-27 Saint Paul Paul lists about a dozen different ways he might have physically died or have been lost (at sea).
Without Jesus Christ the pagans were spiritually dead and spiritually lost. The pagans had many gods. It was so hard to tell if they were pleasing the “right god” at the right time. They even acknowledged the unknown god, to cover that contingency, Acts 17:23.
Jesus gives His followers the gifts of spiritual life and spiritual guidance. We never have to worry about losing our physical life, or of being physically lost, because He gives us these more important gifts of spiritual life and spiritual guidance. In Christ we have security as long as we remain in Christ.
Protestants will often claim a spiritual unity based on their claim to “having a personal relationship with Jesus,” and “being saved by Faith Alone” and by “following the Bible Alone.” However, when they start to define what those vague phrases actually mean the end up splitting into thousands and thousands of denominations.
They have no infallible guidance as to how many books belong in the New Testament, the Bible, or to what the names of those books are. They also have no infallible guidance as to what those books mean (according to their theology) unless they arrogantly assume that only they and their small particular group is sincere in listening to the Holy Spirit.
They are spiritually lost in how to answer many questions. How can a Protestant claim to know that the Bible doesn’t really mean that Baptism really saves us even though the Bible says that it does ?
How can a Protestant claim “to know” that the Bible does not really mean that Jesus gives us His flesh to eat and His blood to drink and that we perish if we do not eat and drink His body and blood when the Bible says that Jesus does do this and that we must eat and drink His flesh and blood ?
God does not want us to be spiritually lost in any way. It is by hearing Jesus’ words and following and trusting in His promises that He gives to the Church He started, that we can have infallible guidance to answer all the important questions we might have.
Christ holds us in his hand (Jn. 10:28) and no one else can forcibly remove us, but we are still free to leave. When we receive Christ we receive the gift of eternal life, but if we later abandon our faith in Christ and reject He who is Life, then we also reject His gift of eternal life.