How is it eternal when it is a present assurance?
The life you receive is eternal, not the assurance that you will always possess it, no matter what, up to the day you die.
You won't eternally possess Christ's life that is eternal until you pass from this life.
Then nothing can ever remove you from the kingdom.
That is the hope that we look and long for.
I am presently assured but I may not be assured in the future. That for me creates a sense of doubt and places a lot of pressure on me.
You only need to be concerned about it to the extent that Paul talks about that:
"20 ...you stand by faith. Do not be arrogant, but tremble. 21For if God did not spare the natural branches, he will not spare you either.
22Consider therefore the kindness and sternness of God: sternness to those who fell, but kindness to you, provided that you continue in his kindness. Otherwise, you also will be cut off." - Romans 11: 20-22
Keep relying on God to encourage and strengthen your faith. Only with God's help and encouragement can you or I keep believing.
What are the sins that can make me loose the Faith?
What sins can make you lose the Faith? The sins you commit in unbelief.
But all sins committed by the BELIEVER are graciously covered and removed by the blood of Christ they believe in. The blood of Christ prevents the believer's sins from separating them from him. That's why we should continue to believe in him:
"14Therefore, since we have a great high priest who has ascended into heaven, f Jesus the Son of God, let us hold firmly to the faith we profess." - Hebrews 4:14
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