The gospel is an offense to a dark world. The good
news that brings such joy to the Christian is a stench
in the nostrils of those who reject it.

I Peter 2:6-8 conains partial quotes from Isaiah 8:14
and Isaiah 28:16.

Therefore it is also contained in the Scripture,
"Behold, I lay in Zion
A chief cornerstone, elect, precious,
And he who believes on Him
will by no means be put to shame."Therefore, to you who believe, He is precious; but
to those who are disobedient,
"The stone which the builders rejected
Has become the chief cornerstone." and
"A stone of stumbling and a rock of offense."

Jesus, Himself, recognized he was an offense to the
pride of many people around Him.

Matthew 13:57 tells us this.

So they were offended at Him.

Jesus asked His disciples in John 6:61, after speaking
to them about the ramifications of His death.

"Does this offend you?"

Paul speaks to this also in Galatians 5:11. He says:

And I, brethren, if I still preach circumcision, why
do I still suffer persecution? Then the offense of
the cross has ceased.

There are several reasons the gospel is an offense.
The main one is the pride of man. Man does not want
to admit that he is unable to be good. He does not
want to have to lay himself down prostrate before
a holy God and say, "I am nothing; You are all."

But...

Just because the message we, as Christians, bring to
the world is offensive to them, it does not mean that
we are to be offensive. Our part is to be gracious
and loving. Our part is to look for opportunities
to shed a word of truth (hard truth though it may be)
in a manner that is calculated to be pleasing. Let
the world be offended by that truth if they will, but
may they not be offended by an ungracious or prideful
attitude in me, the messenger. This is not to say
Christians need to look and act like the world. But,
it is to say that we need to portray the message of
salvation with grace, dignity and love.

Paul understood the Gospel would offend many of those
to whom he presented it. Yet, that did not stop him
from penning the following words in I Corinthians 10
verses 19-22.

For though I am free from all men, I have made
myself a servant to all, that I might win the
more; and to the Jews I became as a Jew, that
I might win the Jews; to those who are under
the law, as under the law, that I might win
those who are under the law; to those who are
without law, as without law (not being without
law toward God, but under law toward Christ),
that I might win those who are without law;
to the weak I became as weak, that I might
win the weak. I have become all things to
all men, that I might by all means save some.

So, we are to be an unoffensive people presenting
a message of great offense.