Everything that the Father gives Me will come to Me, and the one who comes to Me I certainly will not cast out. For I have come down from heaven, not to do My own will, but the will of Him who sent Me. And this is the will of Him who sent Me, that of everything that He has given Me I will lose nothing, but will raise it up on the last day. For this is the will of My Father, that everyone who sees the Son and believes in Him will have eternal life, and I Myself will raise him up on the last day.” John 6:37-40 NASB

Here Christ tells us that the will of God for Believers is that we be raised to eternal life through Jesus. And He declares that He will raise them up on the last day, delivering on God’s Will.

And then there is this. On the night before His crucifixion He prays this prayer to God, His father (The High Priestly Prayer):

“I have revealed Your name to the men whom You gave Me out of the world; they were Yours and You gave them to Me…. I ask on their behalf; I do not ask on behalf of the world, but on the behalf of those whom You have given Me, because they are Yours; and all things that are Mine are Yours, and Yours are Mine; and I have been glorified in them. I am no longer going to be in the world; and yet they themselves are in the world, and I am coming to You. Holy Father, keep them in Your name, the name which You have given Me, so that they may be one just as We are. While I was with them, I was keeping them in Your name, which You have given Me; and I guarded them, and not one of them perished except the son of destruction, so that the Scripture would be fulfilled. John 17:6-12 NASB

Follow the thread. Jesus is praying for the Disciples (and by extension all Believers). “You have given Me these of Your creation as a gift. I have preserved them. But now I am leaving them here. I pray You keep them.“

Jesus prays that Believers be preserved. It is a total insult to the character of God for you to think you could lose your salvation. Jesus prays to God, “Hold on to them. Keep them.” If you were to lose your salvation, that would be an unanswered prayer. Furthermore, God saved you, not primarily for your sake, but for His glory: “I am glorified in them.” For someone to lose their salvation would be a smudge on the glory of God. You have been saved primarily for His glory. So for someone to fall away, it would be ‘what we thought God did He didn’t actually do’ because salvation is not secure. No. Justification is an act of God whereby He declares a sinner to be righteous in His sight based on faith in Christ alone. God does not say one thing and do another. Those who fall away do not lose their salvation. They (including Judas) never had it in the first place. (See here and here)