Andrew Bonar writes to Miss Clarke, offering comfort during her sister's illness by reminding her of the everlasting arms of God that uphold believers in times of trial. He draws parallels between the suffering of Christ and the support the Holy Spirit provides to His followers, assuring her that she is not forgotten. Bonar expresses his desire to visit but acknowledges his current absence due to family commitments, while he continues to pray for their strength and the Lord's presence in their lives.