16 For indeed He does not give aid to angels, but He does give aid to the seed of Abraham.
17 Therefore, in all things He had to be made like His brethren, that He might be a merciful and faithful High Priest in things pertaining to God, to make propitiation for the sins of the people.
18 For in that He Himself has suffered, being tempted, He is able to aid those who are tempted.
indeed (v.16) = doubtless, as is well known
The idea here is that the Lord Jesus, in His work on Calvary’s Cross, did not provide for the salvation of fallen angels but for the salvation of fallen human beings. In perfect righteousness He passed by fallen angels, and in infinite mercy and condescension, stooped to provide salvation for man. For, as is well known, He does not take hold of angels for the purpose of helping them, but of the seed of Abraham He takes hold, with a view to succoring them. — Hebrews in the Greek New Testament, by Kenneth S. Wuest, pages 64-65.
had to be (v.17) — an obligation imposed by reason of a certain consideration — in this case, the position Christ took on as the one who would help lost humanity
merciful (v.17) — sympathy with another’s misery that leads one to act to relieve the misery
faithful … in things pertaining to God (v.17) — the function of worship performed by a priest — in this case, making reconciliation — translated “propitiation” in Romans 3:25.
Because of the perfect union between His two natures, the Lord Jesus is “a merciful and faithful High Priest”: “merciful” man-wards, “faithful” God-wards … Having trod the same path as His suffering and tried people, Christ is able to enter into their afflictions … To be “faithful” means that His compassions are regulated by holiness, His sympathies are exercised, according to the requirements of God’s truth. There is a perfect balance between His maintenance of God’s claims and His ministering to our infirmities. — An Exposition in Hebrews, by Arthur W. Pink, page 90.
the seed of Abraham (v.17) — believers in Christ (Galatians 3:29)
The emphasis in this verse (v.18) is not upon the fact that the Lord Jesus suffered, but upon the fact that He was tempted. The order of the Greek words and their translation are as follows: “For in that which He suffered, having Himself been tempted.” The words : “in that which He suffered” qualify the word “tempted.” the phrase explains in what the temptation consisted. The word “tempted” is the translation of peirazomai, which referred first to the action of putting someone to the test to see what good or evil is in the one tested, and second, because so many broke down under the test and committed sin, the word came to mean a “solicitation to do evil.” Both meanings are in view here. Our Lord in His incarnation as the Last Adam, was put to the test and was also solicited to do evil (Matthew 4:1-11). — Wuest, page 66.
able (v.18) = fit and willing
aid (v.18) = to run to the cry of those in danger and bring them help