salvation is a free gift. Can you loose a gift? Yes you can, is it Jusus' falt you lost it? No.
True, no force from "ouside" is able to steel us from Christs hand, but sice we have free will we can deside to leave faith (for whatever reason)
Read following verses:
*For if we sin wilfully after that we have received the knowledge of the truth, there remaineth
no more sacrifice for sins (lost salvation)
*For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall
fall away, (lost salvation) to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
*If we suffer, we shall also reign with him: if we deny him, he also
will deny us
lost salvation)
*For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body. For this cause many are weak and sickly among you, and many
sleep. (lost salvation)