The Watchtower (and old-timers in the org) love to quote old testament passages that were directed toward Israel. However, the New Testament is "a better covenant based upon better promises".
In the following verses, salvation is not described as a possibility, but as a certainty, as a present possession for the original Christians:
Justification is a present possession (Rom. 5:9).
Peace with God is a present possession (Rom. 5:1).
Reconciliation is a present possession (Rom. 5:10).
Atonement is a present possession (Rom. 5:11)
Eternal life is a present possession (1 Jn. 5:11- 13).
Being a child of God is a present possession (Eph. 1:6).
Being accepted in Christ is a present possession (Eph. 1:6).
Forgiveness of sin is a present possession (Eph. 1:7).
Being made alive in Christ is a present possession (Eph. 2:1).
Being made fit for heaven is a present possession (Col. 1:12).
Being delivered from the power of darkness is a present possession (Col. 1:13).
Having been translated into Jesus’ kingdom is a present possession (Col. 1:13).
Mercy is a present possession (1 Pet. 2:10).
Healing of sin is a present possession (1 Pet. 2:24).
A person is either saved or he is lost, either entirely saved or entirely lost. There is no middle ground, no growing into or perfecting of salvation. Are you trusting the blood of Christ, and the blood of Christ ALONE for salvation? If so, the Bible says you possess all the spiritual blessings listed above, plus much more!
Why isn't the Watchtower proclaiming this Good News?