Paul is a receiver of grace and apostleship (1:5). Paul brings out a number of issues in this text.
The phrase “Though whom” connects verses 4 and 5. Clearly, Paul is a receiver by the means of Jesus Christ. It reveals the continued activity of Christ and indicates that God is the source (cf. 1 Cor. 1:9; Gal. 1:1). Some downgrade this phrase, saying it is “scarcely necessary.” “Though whom” or “by whom (KJV) is the preposition genitive, dia, signifying immediate agency or instrumentality. Wallace identifies it as a genitive of production which produces the nouns (grace and apostleship).
The main verb is the word “received,” which means to take in hand, thus, to receive as a gift. It applies directly to Paul. It is used with the word “we,” an epistolary plural, which we would call an editorial “we” and refers to Paul alone. It speaks of Paul, who alone is the Apostle to the Gentiles (cf. 1:8-16; 11:13)
What he received is identified by the two main nouns: The nouns of grace and apostleship entail his mission and area of responsibility. They specify the awareness that his ministry is unique to the Gentiles (cf. 1:8-16). He states clearly in verse 5 that his ministry for all the Gentiles. There is some debate on the understanding of these two nouns. Either way is permissible. Some understand these as two distinct things: grace and apostleship. Others take it as a hendiadys denoting grace-apostleship. If this is correct, it certainly signifies that the apostleship was a gift of grace. However, Haldane is probably correct that gracious gifts to be used in His service.
The purpose of grace and apostleship to Paul is “to bring about [the] obedience of faith” (1:5). The phrase conveys an evangelistic element. It is used both at the beginning of the epistle and at the end (16:26). Gentile obedience has particular reference to the ministry of Paul and his gospel or apostleship (15:18). Paul received grace and the gracious gift of apostleship for the purpose of obedience of faith. It gives the essence of Paul’s ministry. The phrase itself has given way to a number of interpretations, which Longenecker contributes to the uncertainty of the meaning of the genitive (of faith). He identifies 5 ways in which it could be taken, but he takes it as a genitive of source. Thus, the obedience that comes from faith. However, it seems that most take it as a genitive of apposition. Moo makes these two statements the same: “This obedience to Christ as Lord is always closely related to faith, both as an initial, decisive step of faith and as a continuing faith relationship with Christ. In light of this, we understand the words obedience and faith to be mutually interpreting; obedience always involves faith, and faith always involves obedience.” Godet says, “The only possible meaning is: the obedience which consists in faith itself.” Obedience and faith in apposition are common in this epistle: Rom. 1:8; 16:19, 10:16; 11:23, 30, 31; 15:18. It is the believer’s response to the gospel of grace, especially the Gentile aspect of the gospel.
The object of this mission to bring obedience of faith “among all the Gentiles” (1:5). Paul’s apostleship was a Gentile apostleship (Rom. 11:13; Eph. 3:1-10). Only Paul has such an apostleship…it was unique, directed, and focused upon the Gentiles. The core of “obedience of faith’ is a part of the mystery/secret (Rom. 16:25-26). It is a manifestation of the mystery. It is the substance of Gentile eternal salvation. It is a realization of the dispensation of grace (Eph. 3:2-3). The heart of its content is the equality of Jew and Gentile (Eph. 3:6). “Paul’s commission is to be viewed as other less than the eschatological actualization of the eternal plan to create faith’s obedience among the nations” (Eph. 3:10-12)
It should not be limited to the Pauline mission but includes ethical elements as well. This involved obedience, which is an ethical demand. Surely, the phrase included an ethical sidestep to the Law. As Garlington states:
Whereas before to be a member of the covenant people was to live within the boundary set by the law, the eschatological people have assumed a new corporate identity. And since there is now “no distinction” between Jew and Gentile (1:16-17; 2:11; 10:12; etc.), Paul endeavors in Romans to expound the ethical and social expression of this new corporate entity.
The ethical demand centers upon the phrase “obedience to the faith.” “Faith obedience is set in vivid contrast with legal obedience” correctly states Welch. It is now by faith, not the law, which controls this new corporate body. In every occurrence in Romans obedience has reference to Christian behavior (cf. 2:8, 5:19; 6:12, 16-17). Ethical obedience has the essence of faith. This is clear in Paul, indicating disobedience is equivalent to unbelief (cf. Rom 10:16, 21; 11:23; 15:31).
 C.E.B. Cranfield, ICC: ROMANS, [Edinburgh, T&T Clark, 1975], 1:66
 Daniel B Wallace, GREEK GRAMMAR: BEYOND THE BASICS, [Grand Rapids MI, Zondervan, 1996], 105-106.
 C.E.B. Cranfield, ICC; ROMANS, 1:66;
 This “gives voice to the design of the apostles missionary gospel” notes D.B. Garlington, “The obedience of Faith in the Letter to the Romans,” Part 1; WESTMINSTER THEOLOGICAL JOURNAL 52, 1990, 201.
 Richard N. Longenecker, NIGTC: ROMANS, 79-80; See Cranfield, ROMANS, 1:66 for seven options.
 Douglas J. Moo, NICNT: ROMANS, 54.
 F. Godet, COMMENTARY ON THE EPISTLE TO THE ROMANS, [Grand Rapids MI, Zondervan, reprint 1956], 82.
 D,B. Garlington, The Obedience of Faith,” Part 1, 205.
 IBID, Part 1, 202.
 Charles H. Welch, JUST AND THE JUSTIFIED, [London, Berean Publishing Trust, reprint 1971], 9.