The agent of salvation is the Spirit of God that brings conviction and leads us to Jesus Christ, but the Savior is Jesus Christ.
The Law (the old covenant) required atonement through the blood for the type of offense committed by man. By transferring the dominion and the kingdom of God on earth to satan, the enemy of God, man committed High Treason which must be satisfied in full by capital punishment. Now, God is a just God. He cannot prosecute or punish the devil that rebelled against Him, but look the other side when man did the same thing.
Under the law, atonement is usually by sacrifice, but the blood of bull and calf is limited in efficacy, only the blood of a just and sinless person with active spirit can pay for the offense of a sinner and achieve the remission of sin. That is to completely blot out the sin of man.
Jesus Christ was the only one that was tempted in all ways but did not sin and therefore qualified to be the savior. 2 Corinthians 5:21; For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him.
John 14:6; Jesus said to him, “I am the way, the truth, and the life. No one comes to the Father except through Me.,
Acts 4:10-12; let it be known to you all, and to all the people of Israel, that by the name of Jesus Christ of Nazareth, whom you crucified, whom God raised from the dead, by Him this man stands here before you whole.
This is the ‘stone which was rejected by you builders, which has become the chief cornerstone. Nor is there salvation in any other, for there is no other name under heaven given among men by which we must be saved.”