I am continuing to receive much benefit from Martyn Lloyd-Jones' sermons on the Christian's new life, as published in Experiencing the New Birth (Crossway, 2015). The following highlights are from the sermons about knowing the Triune God, and about the joy that comes from the assurance of salvation...
What is Christianity? Christianity is that which brings a man or woman to a knowledge of God. Take our Lord’s own definition of eternal life: “This is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent.” That is Christianity—knowing God, not just believing a few things about God and living a nice little life. That is not Christianity. That is often nothing but morality or mere religion. The essence of this is entering into this realm into which you begin to know and have communion with the Father and the Son and the Holy Spirit.
The best way to thank him for what he did and what he suffered on your behalf is to enjoy these things that he has given you.
“And these things write we unto you, that your joy may be full” (1 John 1:4). Full! Why did our Lord die for us? Was it to make us miserable? Some people give the impression that the main effect of their being Christians is that they are miserable.
Religion is always a task, a burden, a knowledge of God that makes one fear; religion always depresses, always makes us unhappy. That is why we must be careful lest we be led back into some organized, institutional religion that keeps people priest-ridden and depressed and in the fear of God in the wrong sense, a craven fear. When Martin Luther understood in a flash the doctrine of justification by faith, he began to sing; he was filled with a sense of joy. This is New Testament Christianity.
This is a valuable test: knowing that when everything has gone against you, you still have a spirit of rejoicing within you.
This joy is in Christ, of course. It is not vague and general. The test of whether we are true Christians or not is this: we “worship God in the spirit, and rejoice in Christ Jesus, and have no confidence in the flesh” (Phil. 3:3).
What is a Christian? Well, Christians are men and women who know that they are what they are by the grace of God. Their sins are forgiven. Why? Is it because of their good life or because of their religious duties? Is it because of the gifts they give to others? No, that is religion. Christians know that they owe everything to the grace of God in our Lord and Savior Jesus Christ. They have received it all as a free gift. They know they are what they are—they have forgiveness, new life, everything—because the Son of God gave himself for them on the cross on Calvary’s hill and endured the shame, the suffering, and the agony of it all in order that they might be forgiven and become children of God. Now if you can believe a thing like that and not feel grateful and thankful, then I do not understand you. It is impossible.
“These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life.” My friends, we are meant to know it. We are meant to enjoy it while we are still in this world. Anything short of that is really the spirit of bondage.