[George Cutting answered this better than I could in "Safety, Certainty and Enjoyment." All emphases mine, added on this day of gladness and celebration!]
How did the firstborn sons of Israel know for certain that they were safe the night of the Passover and Egypt’s judgment? Let us take a visit to two of their houses and hear what they have to say.
We find in the first house we enter that they are all shivering with fear and suspense. We inquire, “What is the secret of all this paleness and trembling?” The firstborn son informs us that the angel of death is coming around the land and that he is not quite certain how matters will stand with him at that solemn moment.
“When the destroying angel has passed our house,” says he, “and the night of judgment is over, I shall then know that I am safe, but I can’t see how I can be quite sure of it until then. They say they are sure of salvation next door, but we think it very presumptuous. All I can do is to spend the long, dreary night hoping for the best.”
“Well,” we inquire, “but has the God of Israel not provided a way of safety for His people?”
“True,” he replies, “and we have availed ourselves of that way of escape. The blood of the spotless and unblemished first-year lamb has been duly sprinkled with the bunch of hyssop on the lintel and two side-posts, but still we are not fully assured of shelter.”
Let us now enter next door. What a striking contrast meets our eye at once! Joy shows on every face. There they stand with girded loins and staff in hand, enjoying the roasted lamb.
What can be the meaning of all this joy on such a solemn night as this? ”Ah,” say they all, “we are only waiting for Jehovah’s marching orders, and then we shall bid a last farewell to the taskmaster’s cruel lash and all the drudgery of Egypt.”
“But wait. Do you forget that this is the night of Egypt’s judgment?”
“We know it well, but our firstborn son is safe. The blood has been sprinkled according to the wish of our God.”
“But so it has been next door,” we reply, “but they are all unhappy because they are all uncertain of safety.”
“Ah,” responds the firstborn firmly, “but we have more than the sprinkled blood, we have the unerring word of God about it. God has said, ‘When I see the blood, I will pass over you.’ God rests satisfied with the blood outside, and we rest satisfied with His word inside.”
The sprinkled blood makes us safe.
The written word makes us sure.
Could anything make us more safe than the sprinkled blood, or more sure than His written word? Nothing, nothing.
Now let me ask you a question.
“Which of those two houses think you was the safer?”
Do you say the second, where all were so happy? No, then you are wrong.
Both are safe alike. Their safety depends upon what God thinks about the blood outside and not upon the state of their feelings inside.
If you would be sure of your own blessing, then listen not to the unstable testimony of inward emotions, but to the infallible witness of the word of God. ”Verily, verily, I say unto you, He that believeth on Me hath everlasting life.”
“O how great thy loving-kindness,
Vaster, broader than the sea!
O how marvelous the goodness
Lavished all on me!
Yes, I rest in thee, Beloved,
Know what wealth of grace is thine,
Know thy certainty of promise
And have made it mine.”