You will keep [him] in perfect peace, [Whose] mind [is] stayed [on You,] Because he trusts in You. (Amplified)
The word 'peace' comes from the Hebrew word shalom (Strongs Greek and Hebrew lexicon). It means
completeness in number,
safety, soundness (in body)
welfare, health, prosperity
peace, quiet, tranquillity, contentment
Soundness in body is received from the Lord by focusing our mind on Him. Isaiah says 'whose mind is stayed on God'.
The word stayed comes from the Hebrew word 'camak' which also means 'stand fast'. It speaks of a consistency and persistence in holding unto God.
Don't let your faith waver, nor give room to the thoughts of satan. Keep your mind stayed on Him and He will bring you peace.
Prayer based on Isaiah 26:3
Lord I thank you for your peace. The soundness you bring to my body. The health of my spirit, soul and body comes from you.
Lord Jesus, help me to keep my focus on your. Let me ponder your goodness, mercy and grace. Help me to concentrate on your great power and your awesome might. I refuse to consider any of the lies satan brings to me.
Lord I thank you for allowing your peace to saturate my life. You give me soundness of body and bring health to my bones. That's your promise to me and I receive it from you.
So shall it be in Jesus name (Amen).