There is no prerequisite to obtaining mercy. There is not a certain behavior or nugget of knowledge that can force God to give you help. It is received. By holding fast to the person of Christ, confirmed by His Word, you will receive mercy and help in your time of need. The entirety of Hebrews is encouraging, and sometimes admonishing you, to not relinquish your confession. Your “gritting teeth, persevering, refusal to give up faith”, is not necessary for God to move on your behalf. It is holding fast to the truth of who He is that causes you to receive mercy and help in your greatest time of need.