Originally posted by DoctorScribbles
How can a Christian determine if his faith is sincere? Does he have to wait until death to find out?
No, a Christian does not have to wait until death to find out. How could he or she rejoice otherwise? A Christian can determine whether his or her faith is sincere by whether or not the assurance of the Holy Spirit is present in their lives, progressively sanctifying them, and bearing the fruit of the spirit (love, joy, peace, longsuffering, etc.).
"For as many as are led by the Spirit of God, these are sons of God. For you did not receive the spirit of bondage again to fear, but you received the Spirit of adoption by whom we cry out, “Abba, Father.” The Spirit Himself bears witness with our spirit that we are children of God, and if children, then heirs—heirs of God and joint heirs with Christ, if indeed we suffer with Him, that we may also be glorified together" (Rom. 8:14-17).
"God... has given us the Spirit as a guarantee. So we are always confident" (2 Cor. 5:5-6).
"Therefore, brethren, having boldness to enter the Holiest by the blood of Jesus, by a new and living way which He consecrated for us, through the veil, that is, His flesh, and having a High Priest over the house of God, let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience and our bodies washed with pure water. Let us hold fast the confession of our hope without wavering, for He who promised is faithful" (Heb. 10:19-23).
EDIT: faith itself gives this assurance. "The evidence of things not seen..." (Heb. 11:1).