5 For there is one God and one Mediator between God and men, the Man Christ Jesus,
6 who gave Himself a ransom for all, to be testified in due time,
one God (v.5) — This is not a statement of the existence of one God in contrast to the plurality of the gods of the heathen, as in 1:17, but is designed to lay stress upon the oneness of the relations of God to man. There is not one God for the Jew exclusively.
That’s the point of the connection with the preceding verses, with the injunction that prayer is to be made for all men, and that God “willeth that all men should be saved.” The same truth is enforced in Romans 3:29-30. There the apostle points out that faith is not a national quality and that God s not merely a national God, that “God is one,” i.e., for both Jew and Gentle. There the condition of justification is stressed; here the fact of salvation. In each place the stress on the “one,” marked by its position at the beginning of the sentence, has this force. — Vine, page 158
Mediator (v.5) — acts between two parties with a view to procuring peace
The word “man” explains how Christ Jesus could be a mediator. He can only be an adequate mediator whose sympathy with, and understanding of both parties is cognizable by and patent to both.
The word “mediator” is mesites, “one who intervenes between two, either in order to make or restore peace and friendship, or to form a compact or ratify a covenant.” Our Lord is a mediator in that He interposed Himself by His death, and made possible the restoration of the harmony between God and man which had been broken by sin. — Wuest, page41
Man (v.5) — emphasized in the original to point out the Lord’s humanity and His deity — “Himself Man”
Christ Jesus (v.5) — to emphasize His deity, God who stooped to become man
gave (v.6) — a voluntary act
ransom (v.6) = Greek antilutron — corresponding to a ransom, equivalent in value to that which is procured by it, a payment given instead of (a slave or prisoner), in substitution for
for (v.6) = on behalf of
So “ransom for” refers to payment for and on behalf of …
The word “for” translates huper, which means “on behalf of.” In Matthew 20:28 and Mark 10:45 the preposition is anti, which is of substitutionary significance, and there the accompanying phrase is “for many.” Christ died on behalf of all men; the validity of His sacrifice is universal; but not all men avail themselves of the benefit. It may not be said of the unrepentant sinner that Christ died (anti) in his stead; it can be said that He died on his behalf (huper); hence the limiting phrase in the two passages mentioned. — Vine, page 160
time (v.6) = season, seasonable, suitable for the purpose and characteristic of the period