The cross is the heart of the gospel. It makes the gospel good news: Christ has died for us. He has stood in our place before God’s judgment seat. He has borne our sins. God has done something on the cross which we could never do for ourselves.
But God does something to us as well as for us through the cross. He persuades us that He loves us…God accepts us for Christ’s sake. But He wants to go further. He intends to persuade us that He does accept us for Christ’s sake. So He demonstrates, by adequate proof, His love for us. When I look at the cross, I learn to say ‘The Son of God loved me, and gave Himself for me’ (Galatians 2:20). I begin to believe with Paul that if God did not spare His own Son, but gave Him up to the cross for me, then He loves me so much He will always give me only what will bring me blessing (Romans 8:32).
Such conviction is a key point in Christian growth. If we have deep-seated fears that God does not really love us (as many Christians have), we can only go so far in growing nearer to God. There will come a point at which we will fear to trust Him any further because we cannot be sure of His love. When we look at ourselves, or our own faith, or our circumstances we will never be free from those lurking fears. Satan will see to that. But when we lift up our eyes and look on the cross we find the final persuasion that God is gracious towards us. How can He be against us when all His wrath against us fell upon Christ? How can He fail to care for us when He gave the only Son He had for our sake? How can we doubt Him when He has given us evidence of His love sufficient to banish all doubts?
The reason we lack assurance of His grace is because we fail to focus on that spot where He has revealed it. But if we fail to focus our understanding there, we will fail to grow in grace.
~ Sinclair Ferguson in Grow in Grace, pp. 58-58