If the Lord were pleased to kill us, he would not have received a burnt offering and a meat offering at our hands, neither would he have showed us all these thing. (Judges 13:23)
This is a sort of promise deduced by logic. It is an inference fairly drawn from ascertained facts. It was not likely that the Lord had revealed to Manoah and his wife that a son would be born to them and yet had it in His heart to destroy them. The wife reasoned well, and we shall do well if we follow her line of argument.
The Father has accepted the great sacrifice of Calvary and has declared Himself well pleased therewith; how can He now be pleased to kill us! Why a substitute if the sinner must still perish? The accepted sacrifice of Jesus puts an end to fear.
The Lord has shown us our election, our adoption, our union to Christ, our marriage to the Well-beloved: how can He now destroy us? The promises are loaded with blessings, which necessitate our being preserved unto eternal life. It is not possible for the Lord to cast us away and yet fulfill His covenant. The past assures us, and the future reassures us. We shall not die but live, for we have seen Jesus, and in Him we have seen the Father by the illumination of the Holy Ghost. Because of this life-giving sight we must live forever. - From Faith's Checkbook by C.H. Spurgeon