The Church of God cites Hebrews 9:28 to claim that Jesus appeared a second time in the flesh, but this is a distortion of the Bible. What Paul was trying to convey through Hebrews was that Jesus had fulfilled all of the Old Testament laws and therefore did not need to come back in the flesh and die.

[Hebrews 9:27~28] And as it is appointed unto men once to die, but after this the judgment: So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.

Just as there are many false Christs today, there were many false Christs then, and Paul testified through the law to the fact that Jesus would never come in the flesh in order to expose their false claims.

[2 Thessalonians 2:3~4] Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition; Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.

[1 John 2:18] Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time.

Thus, the context of the entire book of Hebrews is to emphasize that Jesus fulfilled all the law, so there was no need for him to come again in the flesh or die as a sacrifice for sin.

[ Hebrews 9:25~28] Nor yet that he should offer himself often, as the high priest entereth into the holy place every year with blood of others; For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself. And as it is appointed unto men once to die, but after this the judgment: So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.

Therefore, the Bible testifies that Jesus' return will be in spirit, not in body, and will not be visible to all, but will be received by a special group of people.

[Hebrews 12;14] Follow peace with all men, and holiness, without which no man shall see the Lord:

Thus, the Second Coming to which the book of Hebrews testifies refers to a coming in the form of a divine spirit, not a physical body.