Assurance is partially sustained by objective evidences for Christian truth. "To [his apostles] He also presented Himself alive after His suffering, by many convincing proofs, appearing to them over a period of forty days" Acts 1:3.
Assurance cannot neglect the painful work of self-examination. "Test yourselves to see if you are in the faith; examine yourselves! Or do you not recognize this about yourselves, that Jesus Christ is in you - unless indeed you fail the test?" 2 Corinthians 13:5.
Assurance will diminish in the presence of concealed sin. "When I kept silent about my sin, my body wasted away through my groaning all day long" Psalm 32:3.
Assurance comes from hearing the Word of Christ. "So faith comes from hearing, and hearing by the word of Christ" Romans 10:17.
"These have been written so that you may believe that Jesus is the Christ, the Son of God; and that believing you may have life in His name" John 20:31.
Repeated focusing on the sufficiency of the cross of Christ is crucial for assurance. "Since we have a great priest over the house of God, let us draw near with a sincere heart in full assurance of faith" Hebrews 10:21-22.
We must pray for eyes to see the truths that sustain assurance. "I pray that the eyes of your heart may be enlightened, so that you will know what is the hope of His calling, what are the riches of the glory of His inheritance in the saints, and what is the surpassing greatness of His power toward us who believe" Ephesians 1:18-19.
Assurance is not easily maintained in personal isolation. "And the eye cannot say to the hand, 'I have no need of you'" 1 Corinthians 12:21.
Assurance is not destroyed by God's displeasure and discipline. "Do not rejoice over me, O my enemy. Though I fall I will rise; though I dwell in darkness, the LORD is a light for me. I will bear the indignation of the LORD because I have sinned against Him, until He pleads my case and executes justice for me. He will bring me out to the light, and I will see His righteousness" Micah 7:8-9.
We must often wait patiently for the return of assurance. "I waited patiently for the LORD; and He inclined to me and heard my cry. He brought me up out of the pit of destruction, out of the miry clay, and He set my feet upon a rock making my footsteps firm. He put a new song in my mouth, a song of praise to our God; many will see and fear and will trust in the LORD" Psalm 40:1-3.
Assurance is a fight to the day we die. "Fight the good fight of faith; take hold of the eternal life" 1 Timothy 6:12.
"I have fought the good fight, I have finished the course, I have kept the faith" 2 Timothy 4:7.
Assurance is finally a gift of the Spirit. "The Spirit Himself testifies with our spirit that we are children of God" Romans 8:16.
"The one who believes in the Son of God has the testimony in himself... And the testimony is this, that God has given us eternal life, and this life is in His Son" 1 John 5:10-11.