The Gospel is under attack every day, both from within and from without. It is constantly under attack from within from nominal/psuedo "Christians" trying to play Christian instead of actually being Christian. These attacks come in the forms of the charismatic movement, the self-esteem movement, the seeker-sensitive movement, the emergent movement, etc. The Gospel is under attack from those nominal/psuedo "Christians" who do not know their Bible and who are not faithful and obedient to the Lord Jesus, who embrace things like homosexuality, being unable or unwilling to identify sin as sin, take a stand, and call it out. These people are nothing like the Saviour they profess to know.
Decades of having abandoned sound Christian catechisms (such as the Westminster and Heidelberg), coupled with shallow preaching, cultural accommodation, and theological cowardice, have not only left the church wide open to false systems of theology such as Dispensationalism, which filled a void in the church created by Liberalism, but have also left professing Christians lazy and ignorant as to the Word of God. Most professing "Christians" will be surprised when they find themselves in Hell for all eternity because they thought themselves Christians when they refused to repent, believe, and be obedient to the will of the Father.
Jesus made it clear that we should "seek first His Kingdom and His righteousness" (Matt. 6:33) in our own lives, and that only "he who does the will of My Father Who is in Heaven will enter into Heaven" (Matt. 7:21). If you do not "repent and believe in the Gospel" (Mark 1:15), then "unless you repent, you will all likewise perish" (Luke 13:3, 5). Jesus did not say things just for the sake of saying them. He did not love the sound of His own voice the way many false preachers and teachers today do. He meant everything that He said. If you profess to be a genuine Christian, then you must believe this. Everything Jesus said was true. Sadly, many who claim the name of the Lord deny His own words and teachings, proving that they have never belonged to Him and that their eternal abode shall be in darkness in the pit of Hell, rightfully deserved.
The Gospel teaches that Jesus came to save those who could not save themselves; that Jesus paid for our sins. What we need to do in order to receive that is to repent (turn from our sins and turn to God, doing a complete 180, forsaking our sins) and believe in the Gospel. We need to obey the will of the Father. If the Bible says something, it had best be a reality and truth in your life. If it is not, you should be praying for it to become such. The entire New Testament is instructions on how to be a proper and genuine Christian. As John Owen once said, "Obedient faith is that which saves." As the epistle of James makes abundantly clear, empty faith will save you from nothing.
The attacks on the Gospel from without are fairly easy to recognize and counter. But the attacks on the Gospel from within are more subtle and less obvious to those who never spend a day in prayer or read God's Word; to those who do not and have never known God.
It is one thing for you to claim to know God, for you to claim to know Jesus, but does He know you...? (See Matt. 7:21-23)