Wherefore in all things it behoved him to be made like unto his brethren, that he might be a merciful and faithful high priest in things pertaining to God, to make reconciliation for the sins of the people. (Heb 2:17)
There are a number of interesting things when one examines this verse. Firstly, there are two “purpose clauses” in this verse; the first (“that he might be a merciful high priest”) is the Greek ινα clause; the second is the use of the Greek preposition εις which means “into” or “with a goal towards” and this is coupled with the present infinitive form of the verb ιλασκομαι “to make atonement” (ιλασκεσθαι), and this present “making of atonement” is “for the sins of the people” (τας αμαρτιας του λαου). The author of Hebrews views Christ’s on-going office of heavenly intercessor as one that allows for the continuing appeasement of the Father to win the forgiveness of sins committed by believers, sins that were not forgiven at one’s conversion. In other words, this verse presents Jesus as the heavenly high priest who, even at present, makes atonement for sins; this is alien to many theologies that think of one's forgiveness as being once-for-all. The author of Hebrews says Jesus makes atonement for sins on an ongoing basis. If ones’ then-future sins were already atoned for when one appropriated Jesus (esp. if one holds to imputed righteousness), and their justification can never be lost, this verse and its theology is nonsensical. However, Christ's ongoing work as High Priest in the heavenly tabernacle is ongoing in reference to our own sins. Thus, the present infinitive form in Heb 2:17 conclusively demonstrate the continuing need of the application of Christ's work for our own salvation. Reformed Protestants and other proponents of penal substitution and forensic justification are in the unenviable position of having to advocate a soteriology that is at odds with the witness of biblical exegesis
This fits perfectly well with what we find in the Expositor's Greek New Testament (5 vols.), ed. Nicoll Robertson, where Protestant scholar Marcus Dods wrote the following on Heb 2:17:
εἰς τὸ ἱλάσκεσθαι, “for the purpose of making propitiation,” εἰς indicating the special purpose to be served by Christ’s becoming Priest. ἱλάσκομαι (ἱλάσκω is not met with), from ἵλαος, Attic ἵλεως “propitious,” “merciful,” means “I render propitious to myself”. In the classics it is followed by the accusative of the person propitiated, sometimes of the anger felt. In the LXX it occurs twelve times, thrice as the translation of כִּפֵּר. The only instance in which it is followed by an accusative of the sin, as here, is Psalms 64 (65):3, τὰς ἀσεβείας ἡμῶν σὺ ἱλάσῃ. In the N.T., besides the present passage, it only occurs in Luke 18:13, in the passive form ἱλάσθητί μοι τῷ ἁμαρτωλῷ, cf. 2 Kings 5:18. The compound formἐξιλάσκομαι, although it does not occur in N.T., is more frequently used in the LXX than the simple verb, and from its construction something may be learnt. As in profane Greek, it is followed by an accusative of the person propitiated, as in Genesis 32:20, where Jacob says of Esau ἐξιλάσομαι τὸ πρόσωπον αὐτοῦ ἐν τοῖς δώροις κ.τ.λ.; Zechariah 7:2, ἐξιλάσασθαι τὸν Κύριον, and Zechariah 8:22, τὸ πρόσωπον Κυρίου, also Matthew 1:9. It is however also followed by an accusative of the thing on account of which propitiation is needed or which requires by some rite or process to be rendered acceptable to God, as in Sir 3:3; Sir 3:30; Sir 5:6; Sir 20:28, etc., where it is followed by ἀδικίαν, and ἁμαρτίας; and in Leviticus 16:16; Leviticus 16:20; Leviticus 16:33, where it is followed by τὸ ἅγιον, τὸ θυσιαστήριον, and in Ezekiel 45:20 by τὸν οἶκον. At least thirty-two times in Leviticus alone it is followed by περί, defining the persons for whom propitiation is made, περὶ αὐτοῦ ἐξιλάσεται ὁ ἱερεύς or περὶ πάσης συναγωγῆς, or περὶ τῆς ἁμαρτίας ὑμῶν. In this usage there is apparent a transition from the idea of propitiating God (which still survives in the passive ἱλάσθητι) to the idea of exerting some influence on that which was offensive to God and which must be removed or cleansed in order to complete entrance into His favour. In the present passage it is τὰς ἁμαρτίας τοῦ λαοῦ which stand in the way of the full expression of God’s favour, and upon those therefore the propitiatory influence of Christ is to be exerted. In what manner precisely this is to be accomplished is not yet said. “The present infinitive ἱλάσκεσθαι must be noticed. The one (eternal) act of Christ (c. x. 12–14) is here regarded in its continuous present application to men (cf. c. Hebrews 2:1-2).”
