Peterson's two-year-old son died just before the weekend after sustaining injuries consistent with abuse.
The partner of Peterson's ex-wife, Joseph Patterson, was arrested in connection with the death.
But Peterson will play anyway, explaining why in a text to Fox Sports reporter Laura Okmin.
"My brother passed the night before the combine and I decided to go through with it. The same reason why I will play this week.
"You may ask why? God wants good to come from it... We mourn and grieve but heaven had the baddest welcoming party for my son.
"That knowledge gives me peace. I'm still hurt and feel the pain of life, but I'm able to function because of the peace and joy of knowing my loved ones are in a much better place."
Peterson has a history of playing on while grieving, not only when his brother died.
The Vikings are 1-3 and are playing the Carolina Panthers at the Metrodome in Minneapolis on Sunday.