A. You can never lose it even if you make mistakes & fall:

PSA 37:24. Though he fall, he shall not be utterly cast down: for the LORD upholdeth him with his hand.

JOH 3:36. He that believeth on the Son hath everlasting life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him.

JOH 6:37. All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out.

JOH 10:28. And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand.

ROM 8:38. For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come,

ROM 8:39. Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord.

1CO 3:11. For other foundation can no man lay than that is laid, which is Jesus Christ.

1CO 3:12. Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble;

1CO 3:13. Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.

1CO 3:14. If any man's work abide which he hath built thereupon, he shall receive a reward.

1CO 3:15. If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.

1CO 5:5. To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.

HEB 13:5. Let your conversation be without covetousness; and be content with such things as ye have: for he hath said, I will never leave thee, nor forsake thee.

2TI 2:13. If we believe not, yet he abideth faithful: he cannot deny himself.

1JOH 5:13. These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God.

B. But the Lord will chasten you for wrongdoing:

PSA 89:30. If his children forsake my law, and walk not in my judgments;

PSA 89:31. If they break my statutes, and keep not my commandments;

PSA 89:32. Then will I visit their transgression with the rod, and their iniquity with stripes.

PSA 89:33. Nevertheless my lovingkindness will I not utterly take from him, nor suffer my faithfulness to fail.

PSA 89:34. My covenant will I not break, nor alter the thing that is gone out of my lips.

HEB 12:5. And ye have forgotten the exhortation which speaketh unto you as unto children, My son, despise not thou the chastening of the Lord, nor faint when thou art rebuked of him:

HEB 12:6. For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth.

HEB 12:7. If ye endure chastening, God dealeth with you as with sons; for what son is he whom the father chasteneth not?

HEB 12:8. But if ye be without chastisement, whereof all are partakers, then are ye bastards, and not sons.