Particularly, what is 'peace'? I see it from God, with God, of God in the verses below. Are those different variants of peace? I assume that a Christian would know when they are in a state of peace with God. Is this the peace that He gives us (of God)? Should we have this as Christians or do we have to strive for it constantly?

Romans 1:7 Grace to you and peace from God our Father, and the Lord Jesus Christ.

Romans 5:1 we have peace with God through our Lord Jesus Christ

1 Corinthians 1:3
Grace be unto you, and peace, from God our Father, and from the Lord Jesus Christ.

2 Corinthians 1:2
Grace be to you and peace from God our Father, and from the Lord Jesus Christ.

Galatians 1:3
Grace be to you and peace from God the Father, and from our Lord Jesus Christ,

Ephesians 1:2
Grace be to you, and peace, from God our Father, and from the Lord Jesus Christ.

Ephesians 6:23
Peace be to the brethren, and love with faith, from God the Father and the Lord Jesus Christ.

Philippians 1:2
Grace be unto you, and peace, from God our Father, and from the Lord Jesus Christ.

Philippians 4:7
And the peace of God, which passeth all understanding, shall keep your hearts and minds through Christ Jesus.

Colossians 1:2
Grace be unto you, and peace, from God our Father and the Lord Jesus Christ.

1 Thessalonians 1:1
Grace be unto you, and peace, from God our Father, and the Lord Jesus Christ.

2 Thessalonians 1:2
Grace unto you, and peace, from God our Father and the Lord Jesus Christ.

2 Timothy 1:2
Grace, mercy, and peace, from God the Father and Christ Jesus our Lord.

Titus 1:4
Grace, mercy, and peace, from God the Father and the Lord Jesus Christ our Saviour.

Philemon 1:3
Grace to you, and peace, from God our Father and the Lord Jesus Christ.

2 John 1:3
Grace be with you, mercy, and peace, from God the Father, and from the Lord Jesus Christ, the Son of the Father, in truth and love.

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"...with men this is impossible, but with God all things are possible." Matthew 19:26