Some of us, either honestly learning the doctrines of grace from Scripture and struggling with them, or throwing out objections so that they don't have to take them seriously, have asked this question. If you are like me, and you see things like total depravity and unconditional election from Scripture, then you may have struggled with the gospel and with assurance? Perhaps this is owing to me not having a solid foundation upon which to build more meaty doctrines, such as unconditional election. I have no idea. I just know that the particularity of sovereign grace in salvation has at times been a source of comfort and at other times been a great source of confusion, despair, terror, and a stumbling block for assurance.
Here is my attempt to answer the question, "How can I trust in Jesus if I don't know if He came for me or not?" It sounds logical. If Jesus only came for some, and I don't know if I am one of them or not without having God zap me and say, "Tim, you are elect," then how could I ever even trust in Jesus? It seems to strip the basis for trust, kicking the legs out from under it. How could I confidently fall upon Jesus if I don't know if He really came for me? How on earth could I have any assurance that He is truly there for me to rest upon? It sounds like He is there for some and not for others. Unless I have a golden list, and I know my name is on it, why would I have any assurance that He would catch me? Knowing that I need Him is one thing, but knowing that He will catch me is something else.
The answer, as I understand it, is found in the promise of the gospel. I think a fine text to look at, which wrestles with both the promise of the gospel and the sovereignty of God in salvation, is John 6. In this chapter, Jesus explains the unbelief of those who see Him yet don't believe -those He is speaking to when He says, "I am the Bread of life." He says there are those who will come to Him, whom the Father has given Him, and He will turn away none that come to Him. The father draws men to Jesus? How? By supernaturally revealing to them, first, that they are elect? No. By convincing them of their dreadful condition and of the identity and sufficiency of Jesus.
One major point to grasp is that all men are permitted to come to Jesus. Jesus did not keep any back. He even told them to believe in the One the Father sent. Our problem is that we are not able. This is not a physical inability, like that we have a broken leg and can't stand up, even though we really want to. No, this is an unwillingness. It is like when someone has terribly hurt you, and a friend comes and says, "You need to forgive them," but you reply in bitterness and anger, "I can't!" Even if you know you should, your heart is too hardened.
The secont point, with this, is that the promise, "Whoever eats of this Bread will live forever," is objective and sure. It says much. It says that life belongs to all who eat of Him. Those who do see Him as Bread from heaven, the "Bread of Life." The promise serves as its own "invitation," of sorts. If you are a man under the full weight of conviction, knowing that God's wrath awaits you, that you are surely dead if God does not intervene in His mercy, and then Jesus, the One sent by the Father, says this promise in your hearing, you will do what? You will flee to Him. Why? Because in that moment you knew and saw that He is all you will ever need and He is free. The promise assures you that a) you indeed may have Him, and b) you will never lack anything with Him.
Where does the sovereignty of God fit in? Well, why do you think you saw these things? Why did you see Jesus as He is, see your need for Him, hear that promise and believe it, and therefore treasure and embrace Him as your all-in-all? Because the Father drew you. You are not necessarily conscious of it at the time. All you know is your trouble and that Jesus answers it. But it is still nonetheless true that the reason you saw is because of God. God did for you, in His mercy, what He did not do for others.