Once saved always saved?

Many believe that once you are saved you are always saved and that you cannot lose your salvation or be rejected by God.

What is the scriptural basis for “Once saved always saved”? Does not the responsibility lie with the believer how he/she conduct themselves after initially being saved?

I see many scriptures that say/imply other than once saved always saved:

Old Testament:

Num 14:11  Then the LORD said to Moses: "How long will these people reject Me? And how long will they not believe Me, with all the signs which I have performed among them?

Num 14:12  I will strike them with the pestilence and disinherit them..."

1Sa 15:23  For rebellion is as the sin of witchcraft, And stubbornness is as iniquity and idolatry. Because you have rejected the word of the LORD, He also has rejected you from being king."

1Sa 28:6  And when Saul inquired of the LORD, the LORD did not answer him, either by dreams or by Urim or by the prophets.

1Sa 28:7  Then Saul said to his servants, "Find me a woman who is a medium, that I may go to her and inquire of her…"

Pro 2:13  …From those who leave the paths of uprightness To walk in the ways of darkness…

New Testament:

Joh 17:12  …Those whom You gave Me I have kept; and none of them is lost except the son of perdition…

Act 8:9  But there was a certain man called Simon, who previously practiced sorcery…

Act 8:13  …Then Simon himself also believed; and when he was baptized he continued with Philip, and was amazed, seeing the miracles and signs which were done…

Act 8:20  …But Peter said to him, "Your money perish with you, because you thought that the gift of God could be purchased with money!

Act 8:21  You have neither part nor portion in this matter, for your heart is not right in the sight of God.

Act 8:22  Repent therefore of this your wickedness, and pray God if perhaps the thought of your heart may be forgiven you.

Act 8:23  For I see that you are poisoned by bitterness and bound by iniquity."

1Pe 4:17  For the time has come for judgment to begin at the house of God; and if it begins with us first, what will be the end of those who do not obey the gospel of God?

1Pe 4:18  Now "IF THE RIGHTEOUS ONE IS SCARCELY SAVED, WHERE WILL THE UNGODLY AND THE SINNER APPEAR?"

Jas 5:19  Brethren, if anyone among you wanders from the truth, and someone turns him back,

Jas 5:20  let him know that he who turns a sinner from the error of his way will save a soul from death and cover a multitude of sins.

2Ti 2:17  …Hymenaeus and Philetus are of this sort,

2Ti 2:18  who have strayed concerning the truth…

2Ti 2:24  …And a servant of the Lord must not quarrel but be gentle to all, able to teach, patient,

2Ti 2:25  in humility correcting those who are in opposition, if God perhaps will grant them repentance, so that they may know the truth,

2Ti 2:26  and that they may come to their senses and escape the snare of the devil, having been taken captive by him to do his will.

2Pe 2:20  For if, after they have escaped the pollutions of the world through the knowledge of the Lord and Savior Jesus Christ, they are again entangled in them and overcome, the latter end is worse for them than the beginning.

2Pe 2:21  For it would have been better for them not to have known the way of righteousness, than having known it, to turn from the holy commandment delivered to them.

2Pe 2:22  But it has happened to them according to the true proverb: "A DOG RETURNS TO HIS OWN VOMIT," and, "a sow, having washed, to her wallowing in the mire."

Heb 10:26  For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins,

Heb 10:27  but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries.

Heb 10:28  Anyone who has rejected Moses' law dies without mercy on the testimony of two or three witnesses.

Heb 10:29  Of how much worse punishment, do you suppose, will he be thought worthy who has trampled the Son of God underfoot, counted the blood of the covenant by which he was sanctified a common thing, and insulted the Spirit of grace?

Heb 6:4  For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit,

Heb 6:5  and have tasted the good word of God and the powers of the age to come,

Heb 6:6  if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame.