I suppose many do not understand themselves, when they say they want assurance; for what better assurance would you have than the word of God? If you have his word, and take his word, you need no better assurance.
And though the assurance of sense be the sweetest, yet the assurance of faith is the surest assurance; for what you get in hand from God you may soon lose the benefit and comfort of it; but what you have upon bond in the promise, is still secure.
If any man is not sure that he is in Christ, he ought not to be easy one moment until he is sure. Dear friend, without the fullest confidence as to your saved condition, you have no right to be at ease, and I pray you may never be so. This is a matter too important to be left undecided.
If one dear saint of God had perished, so might all; if one of the covenant ones be lost, so may all be; and then there is no gospel promise true, but the Bible is a lie, and there is nothing in it worth my acceptance. I will be an infidel at once when I can believe that a saint of God can ever fall finally. If God hath loved me once, then He will love me forever.
If the faith whereby I have laid hold on Christ to be my Savior be altogether wrought in me by the Holy Ghost through grace, then I defy the devil to take away that which he never gave me or to crush that which Jehovah Himself created in me. I defy my free will to fling what it never brought to me. What God has given, created, introduced, and established in the heart, He will maintain there.
Assurance after all is no more than a full-grown faith; a masculine faith that grasps Christ's promise with both hands - a faith that argues like the good centurion, if the Lord "speak the word only," I am healed. Wherefore then should I doubt? (Matt. 8:8).
Author: J.C. Ryle Source: Holiness, Quoted in: Assured by God, ed. Burk Parsons, PandR, 2006, p. 53.
I believe hundreds of Christian people are being deceived by Satan now on this point, that they have not got the assurance of salvation just because they are not willing to take God at His word.
Now, I find a great many people who want some evidence that they have accepted the Son of God. My friends, if you want any evidence, take God's word for it. You can't find better evidence than that. You know that when the Angel Gabriel came down and told Zachariah he should have a son he wanted a further token than the angel's word. He asked Gabriel for it and he answered, "I am Gabriel, who stands in the presence of the Lord." He had never been doubted, and he thundered out this to Zachariah. But he wanted a further token, and Gabriel said, "You shall have a token: you shall be dumb till your son shall be given you."