John 6:39
John 6:3939And this is the will of Him who sent Me, that I shall lose none of those He has given Me, but raise them up at the last day.
Witnesses are taught that salvation can be lost — by leaving the organisation, by failing the loyalty tests of the great tribulation, by being disfellowshipped. The Watchtower's framework treats final salvation as conditional on continued obedience to Jehovah's earthly channel. Verses about the Father preserving and resurrecting all whom he gives the Son tend to be read as applying narrowly to the 144,000 anointed.
Jesus states the Father's will in three pieces: that the Son should lose none of those given to him, that the Son should resurrect them on the last day, and (verse 40) that everyone who beholds the Son and exercises faith in him should have everlasting life. The first piece is a guarantee of preservation. "Lose none" is total. If a Witness has been given to the Son by the Father, the Son's task — by his own statement of the Father's will — is to keep them, not to chain them to an organisation that will shun them if they leave. The promise sits with the Son's faithfulness, not with their performance. Combine with — no one snatches them out of the Father's hand.