I had never heard of John Main, so I Googled him and what I learned is that John Main's meditation technique is based in Hinduism not Christianity. In other words this Benedictine monk is promoting transcendentalism.
As to dealing with depression:
Philippians 4:4-7
4 Rejoice in the Lord always; again I will say, rejoice! 5 Let your forbearing spirit be known to all men. The Lord is near. 6 Be anxious for nothing, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. 7 And the peace of God, which surpasses all comprehension, shall guard your hearts and your minds in Christ Jesus.
NAS