Forerunner (4274) (prodromos from protrécho = run ahead or before) describes one who goes on ahead to prepare the way. Prodromos was used in Greek to describe one who was sent before to take observations or act as spy or a light-armed soldier soldier sent out ahead of a main force so as to gather information about the enemy’s position, strength, or movements. The prodromos was a scout who was sent out to explore an area and obtain information (much like our modern word "pioneer"). In Paul's day prodromos was the word used to describe the smaller boats that were sent into the harbor by larger ships that were unable to enter due to stormy conditions. These smaller boats or prodomoi carried the anchor through the breakers inside the harbor and dropped it there, securing the larger ship.
A forerunner is defined as one that precedes or is sent as an advance messenger, thus presupposing that others will follow. In this section of Hebrews 6:16-20 the writer dramatically pictures Jesus as not only the believer’s Anchor but as the Runner Boat that has taken our anchor into port and secured it there, in the safety of the "harbor of heaven". Thus every believer can now have complete assurance that his or her "vessel" is going to arrive successfully into the "home port'. Believers in fact now possess such a hope in the presence of God and as stated in Hebrews 4:16 (see note) should come boldly before God's glorious throne of mercy and grace. This is why we may have strong encouragement.
Prodromos is found only here in N.T.
William Barclay writes that
Prodromos, used to describe Jesus, is usually translated “forerunner” and would have had a picturesque meaning for the people of Jesus’ day. The harbor of Alexandria was very difficult to approach. When the great corn ships came into it, a little pilot boat was sent out to guide them in. It went before them, and they followed it as it led them along the channel to safe waters. That pilot boat was called the prodromos. In the Roman army the prodomoi were the reconnaissance troops. They went ahead of the main body of the army to blaze the trail and ensure that it was safe for the rest of the troops to follow. These two things illustrate what Jesus is saying about himself in this passage. He goes first, to make it safe for those who follow. He blazed the way to heaven and to God that we might follow in his steps. (Barclay, W: The Daily Study Bible Series, Rev. ed. Philadelphia: The Westminster Press) (Comment: the prodromos was the smaller boats sent into the harbor by larger ships unable to enter due to the buffeting of the weather. The smaller boats carried the anchor through the breakers inside the harbor and dropped it there, securing the larger ship).
Marvin Vincent adds that prodromos...
expresses an entirely new idea, lying completely outside of the Levitical system. The Levitical high priest did not enter the sanctuary as a forerunner, but only as the people’s representative. He entered a place into which none might follow him; in the people’s stead, and not as their pioneer. The peculiarity of the new (COVENANT) economy is that Christ as High Priest goes nowhere where His people cannot follow Him. He introduces man into full fellowship with God. The A.V. entirely misses this point by rendering “the forerunner,” as if the idea of a high priest being a forerunner were perfectly familiar. (Word Studies in the NT)
Jesus has shown us the way, has gone on ahead, and is the Surety or Guarantor (Hebrews 7:22-note) of our own entrance later. In point of fact, our anchor of hope with its two chains of God's promise and oath has laid hold of Jesus within the veil. It will hold fast. All we need to do is to be true to him as he is to us. Let us hold fast the confession of our faith firm until the end (Hebrews 3:6; Hebrews 4:14 see notes Heb 3:6; 4:14).