It is vitally important that you understand what faith is and what is involved with the act of believing. You must know the distinction between the belief of a demon and the faith of a genuine Believer.

You believe that God is one. You do well; the demons also believe, and shudder. (James 2:19, LSB)

What gives you the confidence that you cannot lose your salvation?

1. Carefully observe who is testifying. What has Jesus witnessed? What is the nature of faith?

"He who comes from above is above all, he who is of the earth is from the earth and speaks of the earth. He who comes from heaven is above all.

What He has seen and heard, of that He bears witness; and no one receives His witness. He who has received His witness has set his seal to this, that God is true.

For He whom God has sent speaks the words of God; for He gives the Spirit without measure. The Father loves the Son and has given all things into His hand. He who believes in the Son has eternal life; but he who does not obey the Son will not see life, but the wrath of God abides on him." (John 3:31-36, LSB)

2. Who is testifying? Make a chart of your observations.

Therefore Jesus answered and was saying to them, "Truly, truly, I say to you, the Son can do nothing from Himself, unless it is something He sees the Father doing; for whatever the Father does, these things the Son also does in the same manner.

For the Father loves the Son, and shows Him all things that He Himself is doing; and the Father will show Him greater works than these, so that you will marvel. For just as the Father raises the dead and gives them life, even so the Son also gives life to whom He wishes. For not even the Father judges anyone, but He has given all judgment to the Son, so that all will honor the Son even as they honor the Father. He who does not honor the Son does not honor the Father who sent Him.

Truly, truly, I say to you, he who hears My word, and believes Him who sent Me, has eternal life, and does not come into judgment, but has passed out of death into life." (John 5:19-24, LSB)