Romans 3:20-21 "because by the works of the Law no flesh will be justified in His sight; for through the Law comes the knowledge of sin.
Hebrews 10:7 records for us God the Son's words as he was coming from eternity into time: "“THEN I SAID, ‘BEHOLD, I HAVE COME (IN THE SCROLL OF THE BOOK IT IS WRITTEN OF ME) TO DO YOUR WILL, O GOD.’” The reader will notice that the quotation is in all caps. The NASB does this to indicate that the quote mirrors an Old Testament text from Psalm 40. The Son of God uttered those words coming from eternity into time. The Son of God did this by way of His incarnation as the man Jesus of Nazareth (Matthew 1:21-23; Luke 1:35; John 1:14; Philippians 2:5-11; Colossians 2:9; Hebrews 2:11-14). As God, Christ's accomplished work of redemption would be enough, since salvation is of the Lord (see Jonah 2:9). As man, Jesus' shedding of blood would provide the price paid for such salvation - called by scripture "redemption" (see Ephesians 1:7). As Romans 3:24 tells us, this willing act of Christ was a work of redemption - that is - He was paying the price for salvation by a willing offering of His human life on behalf of sinners whom the Father loved. So The Father was willing to show mercy and the Son was willing to come, be incarnated as a man and offer Himself up on behalf of sinners. The Father agreed to accept all the the Son accomplished. But now, what about the Holy Spirit?
God the Holy Spirit had to willingly apply the salvation accomplished to those responding in faith to His call.
Romans 3:25-26 notes: "whom God displayed publicly as a propitiation in His blood through faith. This was to demonstrate His righteousness, because in the forbearance of God He passed over the sins previously committed; 26 for the demonstration, I say, of His righteousness at the present time, so that He would be just and the justifier of the one who has faith in Jesus." At this point, one may wonder where the Holy Spirit is in the Romans passage. In as much as Paul is focusing upon the actions agreed upon between the Father and the Son, the Spirit's involvement is implied. Consequently, in later chapters of Romans 5 and 6, we will see explicit mention of the Holy Spirit's activity in applying all that Jesus achieved and the Father authorized.