I agree: the gift of Redemption is free, but we still need to apply effort to keep it. When someone hands me a million dollars, but I get drunk as hell as loose the bag somewhere on the street as I stumble back home, it would still be a free gift, but only a gone gift now
Of course God is so good, that He will give it to me again, if I come to Him again and receive it. The thing about it though, God is not a vending machine, He will not just eject the item upon the pressing of a button, He is a living being, who wants us to grow spiritually, and so He will not always give us eternal life again when we say: "thank you Jesus I receive salvation again now, just faith. Praise you Jesus that I'm saved"! Instead, He might first want us to bring some repentance on the table (Acts 3:19), some sincere regret (2 Corinthians 7:10), before He would do it. And if we don't, we may not feel saved when we say the above, our faith may not receive at that time, because God would just withhold giving us faith, since He is the giver of all good thing.
The reason why some people believe that Salvation cannot be lost, is because they do not understand what it is, or don't know the Scripture. Salvation is Jesus Christ Himself, the Living Word of the Trinity, because He is Eternal Life, and whoever has Him, will not even come to the Judgement (John 5:24). But did not Jesus speak and say to depart from certain people? Did not Apostle Paul also say to depart from certain people? Now, if Jesus is a hypocrite telling us to do what He doesn't do Himself, then fine, but He is not, so He has to obey His own command too. So He WILL leave us if we are a hypocrite or someone who does not "walk" according to the teachings you have read in the New Testament, i.e. if we don't obey those teachings of the New Testament which we came to know. It starts like this: first guilt--a weak throbbing pain of conscience and a sudden flash of understanding of the very thing your conscience is convicting us of. Then, after a short while, boom--He is gone. No longer is there meekness, but arrogance--"I claim, you must!", hatred towards people, wrath, vexatious comments, rudeness and disobedience of every kind.
Most people ignore what their conscience is telling them, they think it's the devil, the accuser, trying to lead them astray from their faith in the irrevocability of Redemption towards them. Not only they sin against the Holy Spirit who it is convicting them through their conscience, giving them guilt, but they also neglect to quickly deal with guilt, to deal with this rush order to repent or perish, before the guilt sours up and rots, and as a hot coal burns a hole in their hearts, causing the Spirit to flow out like wine, their salvation to be lost. They have long seared their conscience in brushing off their guilt, and they do not realize that they are poor, blind and naked.
But by their deeds, by their fruit they can be understood what they are--their own deeds testify of their state.