And this is the record, that God hath given to us eternal life, and this life is in His Son. – 1 John 5:11

Beloved, have you the Son of God? If so, you have life; and even if that life should be somewhat sickly, which is not desirable, yet it will help to make it stronger if you distinctly know that it is the life eternal. When a man’s life becomes feeble, it would be of no service to him to doubt whether it is life at all; but it helps him much to know that it is the life of God, and is therefore sure to be victorious over death and hell, and though it be but a spark, it is such a spark that all the devils in hell cannot tread it out, and all the waters of affliction cannot quench it. If thou hast the Son, poor feeble trembling one, thou hast a life which will co-exist with the life of God; a life which “neither things present, nor things to come, nor height, nor depth, nor any other creature,” shall be able to destroy; because they cannot separate thee from the Lord Jesus; and because He lives, thou shalt live also.

When you begin to doubt your inward graces, and to judge all your past life, and find it wanting, it is sweet even then to say, “One thing I know, I rest in Jesus. Whatever else may be false, this is clearly true-

‘Other refuge have I none,
Hangs my helpless soul on Thee.'”

Job says that the poor man clings to the rock for shelter, and that poor man is blessed who remains in that position, evermore clinging to that Rock of his salvation. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0755.cfm