Is Matthew 6:33 an Absolute Promise of Provision?
Some believers experience poverty even though they seek God's kingdom first. Some suffer because they are followers of Jesus, as they are persecuted by those who are hostile toward Christianity.
We are not guaranteed provision at all times or long life, but we can generally understand this verse to mean we should trust God's sovereignty, that nothing can happen to us outside His plan. God often provides, sometimes even supernaturally in answer to prayer, but when He doesn't, we can trust that He has higher purposes.
We can find security in the fact that God is working all things together for our good, which might not always be the kind of good we are expecting, but our ultimate good from an eternal perspective. While God desires to bless us physically, sometimes He has higher purposes that are spiritual and eternal. He sees that some suffering is necessary for us to grow spiritually, or it may be necessary for us to leave this life- as Paul said, "for to me to live is Christ and to die is gain."
Considering other passages of Scripture such as Romans 8:28-39, Matthew 6:33 may be best interpreted as a general principle rather than an absolute promise of a long life. Our security is not found in what may happen in this life or how long we will live on earth, but in the fact that God is always good and has a plan for us that is eternal.