The fact that the Spirit of Christ in our hearts cries unto God and makes intercession for us with groanings should reassure us greatly. However, there are many factors that prevent such full reassurance on our part. We are born in sin. To doubt the good will of God is an inborn suspicion of God with all of us. Besides, the devil, our adversary, goeth about seeking to devour us by roaring: God is angry at you and is going to destroy you forever. In all these difficulties we have only one support, the Gospel of Christ. To hold on to it, that is the trick. Christ cannot be perceived with the senses. We cannot see Him. The heart does not feel His helpful presence. Especially in times of trials a Christian feels the power of sin, the infirmity of his flesh, the goading darts of the devil, the agues of death, the scowl and judgment of God. All these things cry out against us. The Law scolds us, sin screams at us, death thunders at us, the devil roars at us. In the midst of the clamor the Spirit of Christ cries in our hearts: Abba, Father. And this little cry of the Spirit transcends the hullabaloo of the Law, sin, death, and the devil, and finds a hearing with God.
The Spirit cries in us because of our weakness. Because of our infirmity the Holy Ghost is sent forth into our hearts to pray for us according to the will of God and to assure us of the grace of God.
Let the Law, sin, and the devil cry out against us until their outcry fills heaven and earth. The Spirit of God outcries them all. Our feeble groans, Abba, Father, will be heard of God sooner than the combined racket of hell, sin, and the Law.
Martin Luther, Commentary on Galatians (Kindle Edition, location 2125)