Today's psalm contains an often-quoted line that even appears in the New Testament as relating to the crucifixion of Jesus. Let's read the psalm and then come back to that line.

O give thanks to the Lord, for he is good; his steadfast love endures forever! Let Israel say, “His steadfast love endures forever.” .. Let those who fear the Lord say, “His steadfast love endures forever.” Out of my distress I called on the Lord; the Lord answered me and set me in a broad place. With the Lord on my side I do not fear.    What can mortals do to me? The Lord is on my side to help me; I shall look in triumph on those who hate me. It is better to take refuge in the Lord than to put confidence in mortals. It is better to take refuge in the Lord than to put confidence in princes .. I was pushed hard,[b] so that I was falling, but the Lord helped me. The Lord is my strength and my might; he has become my salvation ..  the right hand of the Lord is exalted; the right hand of the Lord does valiantly. I shall not die, but I shall live, and recount the deeds of the Lord .. Open to me the gates of righteousness, that I may enter through them and give thanks to the Lord .. I thank you that you have answered me and have become my salvation. The stone that the builders rejected has become the chief cornerstone. This is the Lord’s doing; it is marvelous in our eyes. This is the day that the Lord has made; let us rejoice and be glad in it. Save us, we beseech you, O Lord! .. Blessed is the one who comes in the name of the Lord .. The Lord is God, and he has given us light. You are my God, and I will give thanks to you; you are my God, I will extol you. O give thanks to the Lord, for he is good, for his steadfast love endures forever.   (Ps. 118)

What is a cornerstone? The image comes to us from stone quarries where highly trained stonemasons carefully chose stones to be used in construction, particularly the cornerstone. The integrity of the entire building depended upon the cornerstone - if it wasn't right, the building wouldn't be properly aligned and it could collapse. In Matthew 21, Jesus quotes Ps. 118:12 in referring to himself as the cornerstone selected by God. In Acts 4:8-12, the Apostle Peter is preaching to Jewish leaders about Jesus and also quotes this line. Jesus is the "cornerstone" to salvation and Peter tells them that in their rejection of Jesus they have rejected the very One whom God chose to be the cornerstone.  

Jesus is the cornerstone of our faith. He ensures the stability of our faith and our salvation. But notice in the psalm the line that follows: "This is the Lord's doing; it is marvelous in our eyes." When Jesus was predicting his own rejection and death, he quoted those words to his disciples as well. Knowing everything that would happen to him, he called it "marvelous." And it is! So, this is the day that the Lord has made. Let us rejoice and be glad in it! Have a wonderful day.