2 Thessalonians 2:13-15 with some notes in italics -
But we can thank God continually for you, brothers, whom the Lord loves. He has chosen you from the beginning to save you, to make you holy by the work of his Spirit and your own belief in the truth. Or, in other words: There’s a chosenness from the dawn of time that works hand-in-hand with our (in the Greek) “salvation in the sanctification of the Spirit” and our “belief of the truth.” Or, to put it even more simply: Our Belief, while the Holy Spirit does His inner work in us, is our experience of our "chosen" status.
It was his call that you followed when we preached the Gospel to you, and he has set before you the prospect of sharing the glory of our Lord Jesus Christ. So stand firm, and hold on! Be loyal to the teachings we passed on to you, whether by word of mouth or in writings. In essence, Paul is saying to the Thessalonians: “Just believe what you already know.” And what a perfect word for us too, today! You and I must cultivate the abiding, deep and first-hand knowledge of Jesus that we presently possess and then live so as to believe Him.
Living all you know of Him is all you have to do today. It really is just that simple!