In verse 4 we learn the Lord's reply: "This sickness is not unto death, but for the glory of God, that the Son of God might be glorified thereby." If I were either Mary or Martha, I would interpret this is as a promise that my brother would not die. However, we also learn in verse 6 that the Lord stayed were He was for two more days, and verse 14 teaches us that when He arrived, Lazarus has indeed passed away.
In verses 21 and 32, the Bible records Martha and Mary's words to the Lord upon His arrival. They said the same words: "Lord, if thou hadst been here, my brother had not died." We do not have the context behind those words, but we can imagine the anguish of the sisters. Perhaps they wanted to ask why He stayed two more days before coming, or how come He has healed so many but He didn't make it in time to heal a beloved disciple, or even how His promise could possibly have failed?
I believe they said this instead because even in this excruciating trial they both kept their faith. His following conversation with Martha includes one of my favorite passages of scripture in verses 25 and 26:
I am the resurrection, and the life: he that believeth in me, though he were dead, yet shall he live:
And whosoever liveth and believeth in me shall never die. Believest thou this?
Before Jesus raises Lazarus from the dead He promises eternal life, which only Christ can. Even death, as absolute and insurmountable as anything, bends the knee and obeys the will of our Lord. He is teaching that no night is too dark and no burden is too heavy for those who lean on Jehovah for strength.
Martha, though suffering, would not let her pains dim the brilliance of her faith, and she responded: "Yea, Lord: I believe that thou art the Christ, the Son of God, which should come into the world." Martha's response to this potentially disillusioning sequence of events in life was to express faith, even though the Lord just said words that seemed to be directly contradicted by her brother's death.
Shortly after, we read in verses 43 and 44 that the Lord brings Lazarus back to life. The Lord knew all along that He would restore Lazarus' life to him, but Mary and Martha did not. They did demonstrate that no matter what happens they wouldn't lose their faith in Jesus as the Christ.
In life, many things happen which are beyond our comprehension. We will have trials that seem impossible to reconcile with our beliefs and our understanding. I pray, for myself and us all, that we can match the examples of Mary and Martha and follow this council:
36 Look unto me in every thought; doubt not, fear not.I testify that our comfort and our answers lie in following the Savior. He has the words of eternal life.
37 Behold the wounds which pierced my side, and also the prints of the nails in my hands and feet; be faithful, keep my commandments, and ye shall inherit the kingdom of heaven. Amen.