Jesus said very clearly that all the father gives him will not be lost. So when one is saved that person's faith will cause him to endure to the end. You are not taking all of the bible into consideration when you are looking at John 15. Oh, and its unadvisable to use the concordance basic meanings of words as if they always mean only one thing because that is not how Greek thought, grammar and their language works.
Woah woah woah That is not what Jesus said. He never said all the Father gives Him will not be lost. What He actually said was this.
“This is the will of Him who sent Me, that of all that He has given Me I lose nothing, but raise it up on the last day. For this is the will of My Father, that everyone who beholds the Son and believes in Him will have eternal life, and I Myself will raise him up on the last day."”
John 6:39-40 NASB
What is the Greek word translated to will? There’s 2 that are relevant to this passage of scripture, thélēma (G2307) which is the noun form which is used in John 6:39 & 40.
Description:
1) what one wishes or has determined shall be done a) of the purpose of God to bless mankind through Christ b) of what God wishes to be done by us
1) commands, precepts
2) will, choice, inclination, desire, pleasure
Then there’s thélō (G2309) which is the verb form of the same word used in 1 Timothy 2:4.
Description:
1) to will, have in mind, intend a) to be resolved or determined, to purpose b) to desire, to wish c) to love
1) to like to do a thing, be fond of doing d) to take delight in, have pleasure
Both of these words do not always mean some that God has deemed to be so. They can also mean what God desires to be so. 1 Timothy 2:3-4 is a perfect example of this.
“This is good and acceptable in the sight of God our Savior, who
desires all men to be saved and to come to the knowledge of the truth.”
1 Timothy 2:3-4 NASB
So John 6:39-40 can actually be translated
“This is the desire of Him who sent Me, that of all that He has given Me I lose nothing, but raise it up on the last day. For this is the desire of My Father, that everyone who beholds the Son and believes in Him will have eternal life, and I Myself will raise him up on the last day."”
John 6:39-40 NASB
So we see that while God desires all men to repent and be saved that doesn’t mean that He has declared that it will be so. While God also desires all who believe in Christ that He would lose none that also will not be so because as I already stated in John 15:2 Jesus specifically says that The Father cuts off every branch IN ME that beareth not fruit. He also said in John 15:6 anyone who does not abide (stay, remain, continue) in Me is cast away to wither and cast into the fire to be burned. Both verses 2 and 6 can ONLY pertain to believers because no one can be IN CHRIST who does not believe and no one can fail to abide, stay, remain, or continue to be in Christ who has never been in Christ to begin with.
Like you told me earlier understanding the Greek makes a big difference in understanding the message the authors of the NT were actually trying to convey.