Our eternal security does not depend on us. It would be impossible for believers to assure themselves that they belong to God, and that they could never be separated from Him, if it was left up to us to do so. There are too many factors involved that prevent this. Nevertheless, although there could be some that might convinced themselves that they belong to God, or at least 'presume', it is infallibly declared that "the foundation of God standeth sure", and it has "this seal": That "the Lord knoweth them that are his"! In other words, dear beloved in the Lord, all those that the Father has given to His Son, and have come to Him, can have the assurance that the Lord knows them as His. As He said in John 6:37 - "All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out", so that He can also say: "Behold I and the children which God hath given me" (Hebrews 2:13).
But it is imperative that we understand this: The knowing that we
to the Lord, not only comes from His Word (1 John 5:13), and by "the
Spirit itself (bearing) witness with our spirit, that we are the
of God" (Romans 8:16), but also by the way we live! Consider that
text also says: "And, Let every one that nameth the name of Christ
from iniquity". This simply means that if we claim to belong to God
in Christ Jesus, then we are to stay away from anything that is not
for "he that saith he abideth in him", i.e Christ, "ought
also so to walk, even as he walked" (1 John 2:6). Oh, for grace
strength to "depart from iniquity" because we belong to Him.