Can the truly saved lose their salvation?
The short answer is NO! If they depart from Christ and the doctrine of Christ they prove they never were saved. Continuation is the proof and evidence of salvation. True believers will persevere to the end.
True believers can backslide and live temporarily in sin, but they will be chastened and corrected by God, but they will eventually return or be taken to heaven prematurely.
Let's look at some proof passages for continuation as proof of salvation.
Matt. 13:18-23 18 Hear ye therefore the parable of the sower. 19 When any one heareth the word of the kingdom, and understandeth it not, then cometh the wicked one, and catcheth away that which was sown in his heart. This is he which received seed by the way side. 20 But he that received the seed into stony places, the same is he that heareth the word, and anon with joy receiveth it; 21 Yet hath he not root in himself, but dureth for a while: for when tribulation or persecution ariseth because of the word, by and by he is offended. 22 He also that received seed among the thorns is he that heareth the word; and the care of this world, and the deceitfulness of riches, choke the word, and he becometh unfruitful. 23 But he that received seed into the good ground is he that heareth the word, and understandeth it; which also beareth fruit, and bringeth forth, some an hundredfold, some sixty, some thirty.
Note that only the "good ground" [receptive heart] was saved and continued to bear fruit.
Hebrews 3:6 But Christ as a son over his own house; whose house are we, if we hold fast the confidence and the rejoicing of the hope firm unto the end.
Hebrews For we are made partakers of Christ, if we hold the beginning of our confidence stedfast unto the end;
Hebrews And we desire that every one of you do shew the same diligence to the full assurance of hope unto the end:
Hebrews 10:38-39 38 Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him. 39 But we are not of them who draw back unto perdition; but of them that believe to the saving of the soul.
Col. 1:21-23 21 And you, that were sometime alienated and enemies in your mind by wicked works, yet now hath he reconciled 22 In the body of his flesh through death, to present you holy and unblameable and unreproveable in his sight: 23 If ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel, which ye have heard, and which was preached to every creature which is under heaven; whereof I Paul am made a minister;
If ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel, which ye have heard, and which was preached to every creature which is under heaven; whereof I Paul am made a minister;
1 John They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.
Matt. 7:22-24 22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? 23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity. 24 Therefore whosoever heareth these sayings of mine, and doeth them, I will liken him unto a wise man, which built his house upon a rock: