Hebrews tells us the one and perfect sacrifice of Jesus was more than sufficient to make us sinners righteous for all time, not just until we sinned the next time. We cannot sustain or maintain our salvation by our own righteousness. Rather we must believe that God alone secures our salvation and our place of righteousness before Him.

Jesus Himself declared that “no one can snatch us” out of His hand (John 10:28-29). He can confidently say that because God Himself promised to Himself that He will take the full responsibility to guarantee and secure our salvation.

In the same way God, desiring even more to demonstrate to the heirs of the promise the fact that His purpose is unchangeable, confirmed it with an oath, so that by two unchangeable things in which it is impossible for God to lie, we who have taken refuge would have strong encouragement to hold firmly to the hope set before us. This hope we have as an anchor of the soul, a hope both sure and reliable and one which enters within the veil, where Jesus has entered as a forerunner for us, having become a high priest forever according to the order of Melchizedek.

Hebrews 6:17-20 (NASB)

If we are capable of losing our salvation, it was never really salvation at all. It was only a temporary reprieve from God's judgment and anger until we sinned again. Knowing God cannot lie, our confidence of salvation is anchored on two unchangeable things. So just what are these two unchangeable things? First, God's oath and second, God's promise to secure us forever in Jesus. In other words, our salvation rests on God’s word and character.

It is our security in Christ that gives us eternal life and motivates us to live uprightly (Titus 2:11–12). Instead of asking, "what if I failed again as a believer”, you need to be asking, “But what if God has already unconditionally chosen to save me and sanctify me as holy and abide me in Him to the end?” And the answer to that question is a resounding yes. This is why many may say the good news is too good to be true.