Two brief comments on this brief text:
5:9 The major translations differ on how the understand the "ei" clause in verse 9. "Ei" expresses conditionality (if); however, in this case, since the verb in the "ei" clause is in the indicative and not the subjunctive, one can translate the "ei" to mean "since."
The entire passage: The verbs for life are all in the present. Jesus is the life; the one who is believing/having the son is having eternal life. Eternal life and having Jesus are not future activities, but present ones.
There are some verbs in the perfect (testify; make a liar); but the verbs around faith, life and Jesus are all present, implying now and on-going action.