As believers, it seems to us that the Gospel can surely stand on its own two feet. It is an undeniable fact, and does not need to be defended. However, there are many unbelievers, and many seemingly intelligent philosophies, that would not agree with us. We find times when the Gospel must not only be shared, it must also be defended.
What is the Gospel? It is the death, burial, and resurrection of Christ. When Paul defended the Gospel, he could have used a three-fold argument:  The Holy Scriptures taught it;  the testimony of fellow believers; and  the working of the Holy Spirit in his own heart and life. He had multiple opportunities to defend the Gospel
But, notice that he couples this ‘defence of the Gospel’ with ‘grace’. Our defence of the Gospel must be more than merely a theological argument. That kind of reasoning is dead. We may end up winning the battle, but ultimately losing the war—the conversion of a soul to Christ.
The Gospel must be far more than a point of theology. It must be a deeply held, sensitive, experience that we have had with the central Person of the Gospel—Jesus Christ, our wonderful Savior. We see in the Scriptures not only that Christ died, was buried, and rose again, but we are touched to think that all this was for me, an unworthy sinner. We see the power of the Gospel being played out in the lives of fellow believers, and we experience on a daily basis how this risen Christ is walking by our sides.
Our best defence of the Gospel will never be a theological argument. It will be a transparency in our lives where others can see the reality of the Gospel in us.
Even as it is meet for me to think this of you all, because I have you in my heart; inasmuch as both in my bonds, and in the defence and confirmation of the gospel, ye all are partakers of my grace. Philippians 1:7